diff --git a/pkg/analyzer/test/src/dart/analysis/driver_caching_test.dart b/pkg/analyzer/test/src/dart/analysis/driver_caching_test.dart
index 489de5428a7..fb0bab395cf 100644
--- a/pkg/analyzer/test/src/dart/analysis/driver_caching_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/driver_caching_test.dart
@@ -312,7 +312,7 @@ void f() {
 
     // We don't have any lints configured, so no errors.
     var result = await resolveTestFile();
-    assertErrorsInTestResult(result, []);
+    expect(result.diagnostics, isEmpty);
 
     // The summary for the library was linked.
     _assertContainsLinkedCycle({testFile}, andClear: true);
diff --git a/pkg/analyzer/test/src/dart/analysis/driver_test.dart b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
index d25f1c81fbe..10630d0daf4 100644
--- a/pkg/analyzer/test/src/dart/analysis/driver_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/driver_test.dart
@@ -131,7 +131,7 @@ class AnalysisDriver_LintTest extends PubPackageResolutionTest
     var result = await resolveTestFile();
 
     // No errors for a file that doesn't exist.
-    assertErrorsInTestResult(result, []);
+    expect(result.diagnostics, isEmpty);
   }
 
   void _assertHasLintReported(List<Diagnostic> diagnostics, String name) {
diff --git a/pkg/analyzer/test/src/dart/analysis/index_test.dart b/pkg/analyzer/test/src/dart/analysis/index_test.dart
index 1bd2b7686a8..37c9dde14e7 100644
--- a/pkg/analyzer/test/src/dart/analysis/index_test.dart
+++ b/pkg/analyzer/test/src/dart/analysis/index_test.dart
@@ -8,7 +8,6 @@ import 'package:analyzer/source/file_source.dart';
 import 'package:analyzer/source/source.dart';
 import 'package:analyzer/src/dart/analysis/index.dart';
 import 'package:analyzer/src/dart/element/element.dart';
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/test_utilities/find_element2.dart';
 import 'package:collection/collection.dart';
@@ -81,8 +80,10 @@ const myDiagnosticCode = 0;
 import 'diagnostic.dart';
 ''');
 
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'helper.dart';
+//     ^^^^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'helper.dart'.
 
 void f() {
   '// [diag.myDiagnosticCode] message';
@@ -95,14 +96,13 @@ void f() {
   }
 
   test_ClassElement_emptyBody() async {
-    var result = await _indexTestUnit(r'''
+    await _indexTestCode(r'''
 class C;
 ''');
-    assertErrorsInTestResult(result, []);
   }
 
   test_ClassElement_hierarchy_class_extends() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -110,7 +110,6 @@ class A {}
 class B extends A {}
 class B_q extends p.A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -123,7 +122,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_hierarchy_class_extends_implicitObject() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {}
 ''');
     var element = result.typeProvider.objectType.element;
@@ -133,7 +132,7 @@ class A {}
   }
 
   test_ClassElement_hierarchy_class_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -141,7 +140,6 @@ class A {}
 class B implements A {}
 class B_q implements p.A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -154,18 +152,18 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_hierarchy_class_with() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
 
 class D extends Object with A {}
+//                          ^
+// [diag.classUsedAsMixin] The class 'A' can't be used as a mixin because it's neither a mixin class nor a mixin.
 class D_q extends Object with p.A {}
+//                            ^^^
+// [diag.classUsedAsMixin] The class 'A' can't be used as a mixin because it's neither a mixin class nor a mixin.
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.classUsedAsMixin, 66, 1),
-      error(diag.classUsedAsMixin, 101, 3),
-    ]);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -178,18 +176,18 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_hierarchy_classTypeAlias_with() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
 
 class D2 = Object with A;
+//                     ^
+// [diag.classUsedAsMixin] The class 'A' can't be used as a mixin because it's neither a mixin class nor a mixin.
 class D2_q = Object with p.A;
+//                       ^^^
+// [diag.classUsedAsMixin] The class 'A' can't be used as a mixin because it's neither a mixin class nor a mixin.
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.classUsedAsMixin, 61, 1),
-      error(diag.classUsedAsMixin, 89, 3),
-    ]);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -202,7 +200,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_hierarchy_enum_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -210,7 +208,6 @@ class A {}
 enum E implements A { v }
 enum E_q implements p.A { v }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -223,7 +220,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_hierarchy_extensionType_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -231,7 +228,6 @@ class A {}
 extension type E(A it) implements A {}
 extension type E_q(A it) implements p.A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -246,7 +242,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_hierarchy_mixin_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -254,7 +250,6 @@ class A {}
 mixin M implements A {}
 mixin M_q implements p.A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -267,7 +262,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_hierarchy_mixin_on() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -275,7 +270,6 @@ class A {}
 mixin M2 on A {}
 mixin M2_q on p.A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -288,7 +282,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_reference_annotation() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {
@@ -305,7 +299,6 @@ class A {
 @p.A.myConstant
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -322,7 +315,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_reference_annotation_typeArgument() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 class A<T> {
   const A();
 }
@@ -339,11 +332,15 @@ void f() {}
   }
 
   test_ClassElement_reference_classTypeAlias() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {}
 class B = Object with A;
+//                    ^
+// [diag.classUsedAsMixin] The class 'A' can't be used as a mixin because it's neither a mixin class nor a mixin.
 void f(B p) {
   B v;
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'v' isn't used.
 }
 ''');
     var element = result.findElement.class_('B');
@@ -354,7 +351,7 @@ void f(B p) {
   }
 
   test_ClassElement_reference_comment() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -371,10 +368,14 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_reference_definedInSdk() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'dart:math';
 Random v1;
+//     ^^
+// [diag.notInitializedNonNullableVariable] The non-nullable variable 'v1' must be initialized.
 Random v2;
+//     ^^
+// [diag.notInitializedNonNullableVariable] The non-nullable variable 'v2' must be initialized.
 ''');
     var element = result.findElement.importFind('dart:math').class_('Random');
     assertElementIndexText(result, element, r'''
@@ -387,11 +388,13 @@ Random v2;
     newFile('$testPackageLibPath/lib.dart', r'''
 class A {}
 ''');
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'lib.dart';
 
 void f(A p) {
   A v = p;
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'v' isn't used.
 }
 ''');
     var element = result.findNode.namedType('A p').element!;
@@ -402,7 +405,7 @@ void f(A p) {
   }
 
   test_ClassElement_reference_instanceCreation() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -412,7 +415,6 @@ void f() {
   p.A();
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -423,7 +425,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_reference_memberAccess() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {
@@ -435,7 +437,6 @@ void f() {
   p.A.foo();
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -446,24 +447,26 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_reference_namedType() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
 
 void f() {
   A v1;
+//  ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v1' isn't used.
   p.A v2;
+//    ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v2' isn't used.
   List<A> v3;
+//        ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v3' isn't used.
   List<p.A> v4;
+//          ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v4' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.unusedLocalVariable, 53, 2),
-      error(diag.unusedLocalVariable, 63, 2),
-      error(diag.unusedLocalVariable, 77, 2),
-      error(diag.unusedLocalVariable, 93, 2),
-    ]);
 
     var element = result.findElement.class_('A');
     assertElementIndexText(result, element, r'''
@@ -476,7 +479,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ClassElement_reference_recordTypeAnnotation_named() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 class A {}
 
 void f(({int foo, A bar}) r) {}
@@ -488,7 +491,7 @@ void f(({int foo, A bar}) r) {}
   }
 
   test_ClassElement_reference_recordTypeAnnotation_positional() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 class A {}
 
 void f((int, A) r) {}
@@ -500,7 +503,7 @@ void f((int, A) r) {}
   }
 
   test_ClassElement_reference_typeLiteral() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A {}
@@ -517,7 +520,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ConstructorElement_class_method_sameName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A.foo() {
     foo();
@@ -539,8 +542,10 @@ class A {
   }
 
   test_ConstructorElement_class_named_newHead() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A.foo] and [A.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A {
   new foo() {}
   new bar() : this.foo();
@@ -553,12 +558,10 @@ void useConstructor() {
   A.foo();
   A.foo;
   A a = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 200, 1),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -573,8 +576,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_named_primary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A.foo] and [A.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A.foo() {
   new bar() : this.foo();
   factory baz() = A.foo;
@@ -586,12 +591,10 @@ void useConstructor() {
   A.foo();
   A.foo;
   A a = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 191, 1),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -606,8 +609,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_named_typeName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A.foo] and [A.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A {
   A.foo() {}
   A.bar() : this.foo();
@@ -620,12 +625,10 @@ void useConstructor() {
   A.foo();
   A.foo;
   A a = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 195, 1),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -640,8 +643,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_named_typeName_viaTypeAlias() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new B.foo] and [B.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A<T> {
   A.foo() {}
   A.bar() : this.foo();
@@ -655,12 +660,10 @@ void useConstructor() {
   B.foo();
   B.foo;
   B b = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'b' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 218, 1),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -675,8 +678,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_unnamed_implicit() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class B {
   B();
   factory B.baz() = A;
@@ -689,12 +694,10 @@ void useConstructor() {
   A();
   A.new;
   A a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 170, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -708,7 +711,7 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_unnamed_implicitInvocation_fromNewHead() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A();
 }
@@ -717,6 +720,11 @@ class B extends A {
   new ();
   new bar();
   factory new.baz() = A;
+//        ^^^
+// [diag.expectedIdentifierButGotKeyword] 'new' can't be used as an identifier because it's a keyword.
+// [diag.invalidFactoryNameNotAClass] The name of a factory constructor must be the same as the name of the immediately enclosing class.
+//                    ^
+// [diag.redirectToInvalidReturnType] The return type 'A' of the redirected constructor isn't a subtype of 'B'.
 }
 ''');
 
@@ -729,7 +737,7 @@ class B extends A {
   }
 
   test_ConstructorElement_class_unnamed_implicitInvocation_fromTypeName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A();
 }
@@ -738,6 +746,8 @@ class B extends A {
   B();
   B.bar();
   factory B.baz() = A;
+//                  ^
+// [diag.redirectToInvalidReturnType] The return type 'A' of the redirected constructor isn't a subtype of 'B'.
 }
 
 class C extends A {}
@@ -753,8 +763,10 @@ class C extends A {}
   }
 
   test_ConstructorElement_class_unnamed_newHead() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A {
   new () {}
   new bar() : this();
@@ -767,12 +779,10 @@ void useConstructor() {
   A();
   A.new;
   A a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 177, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -787,36 +797,34 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_unnamed_otherFile() async {
-    var other = convertPath('$testPackageLibPath/other.dart');
-    var otherFile = newFile(other, '''
-import 'test.dart';
+    var otherFile = getFile('$testPackageLibPath/other.dart');
 
-void f() {
-  A();
-}
-''');
-
-    var result = await resolveTestCode('''
+    var result = await resolveTestCodeWithDiagnostics('''
 class A {
   A() {}
 }
 ''');
     var element = result.findElement.unnamedConstructor('A');
 
-    result = await resolveFile2(otherFile);
-    index = AnalysisDriverUnitIndex.fromBuffer(
-      indexUnit(result.unit).toBuffer(),
-    );
+    result = await resolveFileWithDiagnostics(otherFile, '''
+import 'test.dart';
+
+void f() {
+  A();
+}
+''');
+    _indexResult(result);
 
-    assertErrorsInTestResult(result, []);
     assertElementIndexText(result, element, r'''
 35 4:4 || IS_INVOKED_BY qualified
 ''');
   }
 
   test_ConstructorElement_class_unnamed_primary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A() {
   new bar() : this();
   factory baz() = A;
@@ -828,12 +836,10 @@ void useConstructor() {
   A();
   A.new;
   A a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 167, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -848,8 +854,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_unnamed_typeName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A {
   A() {}
   A.bar() : this();
@@ -862,12 +870,10 @@ void useConstructor() {
   A();
   A.new;
   A a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 171, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -882,8 +888,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_class_unnamed_typeName_explicitNew() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 class A {
   A.new() {}
   A.bar() : this.new();
@@ -896,12 +904,10 @@ void useConstructor() {
   A.new();
   A.new;
   A a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 191, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -916,14 +922,18 @@ void useConstructor() {
   }
 
   test_ConstructorElement_classTypeAlias() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class M {}
 class A {
   A() {}
   A.named() {}
 }
 class B = A with M;
+//               ^
+// [diag.classUsedAsMixin] The class 'M' can't be used as a mixin because it's neither a mixin class nor a mixin.
 class C = B with M;
+//               ^
+// [diag.classUsedAsMixin] The class 'M' can't be used as a mixin because it's neither a mixin class nor a mixin.
 void useConstructor() {
   B();
   B.named();
@@ -931,10 +941,6 @@ void useConstructor() {
   C.named();
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.classUsedAsMixin, 64, 1),
-      error(diag.classUsedAsMixin, 84, 1),
-    ]);
     var constructor = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, constructor, r'''
 114 9:4 || IS_INVOKED_BY qualified
@@ -949,48 +955,55 @@ void useConstructor() {
   }
 
   test_ConstructorElement_classTypeAlias_cycle() async {
-    var result = await _indexTestUnit('''
+    await _indexTestCode('''
 class M {}
 class A = B with M;
+//    ^
+// [diag.recursiveInterfaceInheritance] 'A' can't be a superinterface of itself: B, A.
+//               ^
+// [diag.classUsedAsMixin] The class 'M' can't be used as a mixin because it's neither a mixin class nor a mixin.
 class B = A with M;
+//    ^
+// [diag.recursiveInterfaceInheritance] 'B' can't be a superinterface of itself: B, A.
+//               ^
+// [diag.classUsedAsMixin] The class 'M' can't be used as a mixin because it's neither a mixin class nor a mixin.
 void useConstructor() {
   A();
   B();
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.recursiveInterfaceInheritance, 17, 1),
-      error(diag.classUsedAsMixin, 28, 1),
-      error(diag.recursiveInterfaceInheritance, 37, 1),
-      error(diag.classUsedAsMixin, 48, 1),
-    ]);
     // No additional validation, but it should not fail with stack overflow.
   }
 
   test_ConstructorElement_enum_named_newHead() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E.foo] and [E.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E {
   v.foo();
   const new foo();
   const new bar() : this.foo();
+//          ^^^
+// [diag.unusedElement] The declaration 'E.bar' isn't referenced.
   const factory baz() = E.foo;
+//                      ^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E.foo();
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.foo;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedElement, 79, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 123, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 158, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 169, 5),
-      error(diag.unusedLocalVariable, 180, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 185, 3),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -1005,28 +1018,33 @@ void useConstructor() {
   }
 
   test_ConstructorElement_enum_named_primary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E.foo] and [E.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E.foo() {
   v.foo();
   const new bar() : this.foo();
+//          ^^^
+// [diag.unusedElement] The declaration 'E.bar' isn't referenced.
   const factory baz() = E.foo;
+//                      ^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E.foo();
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.foo;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedElement, 66, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 110, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 145, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 156, 5),
-      error(diag.unusedLocalVariable, 167, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 172, 3),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -1041,29 +1059,34 @@ void useConstructor() {
   }
 
   test_ConstructorElement_enum_named_typeName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E.foo] and [E.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E {
   v.foo();
   const E.foo();
   const E.bar() : this.foo();
+//        ^^^
+// [diag.unusedElement] The declaration 'E.bar' isn't referenced.
   const factory E.baz() = E.foo;
+//                        ^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E.foo();
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.foo;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedElement, 75, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 121, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 156, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 167, 5),
-      error(diag.unusedLocalVariable, 178, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 183, 3),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -1078,28 +1101,32 @@ void useConstructor() {
   }
 
   test_ConstructorElement_enum_unnamed_implicit() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E] and [E.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E {
   v1,
   v2(),
   v3.new();
   const factory E.other() = E;
+//                          ^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E();
+//^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.new;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 87, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 118, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 125, 5),
-      error(diag.unusedLocalVariable, 136, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 141, 3),
-    ]);
     var element = result.findElement.unnamedConstructor('E');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1115,29 +1142,33 @@ void useConstructor() {
   }
 
   test_ConstructorElement_enum_unnamed_newHead() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E] and [E.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E {
   v1,
   v2(),
   v3.new();
   const new ();
   const factory other() = E.new;
+//                        ^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E();
+//^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.new;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 101, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 136, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 143, 5),
-      error(diag.unusedLocalVariable, 154, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 159, 3),
-    ]);
     var element = result.findElement.unnamedConstructor('E');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1153,28 +1184,32 @@ void useConstructor() {
   }
 
   test_ConstructorElement_enum_unnamed_primary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E] and [E.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E() {
   v1,
   v2(),
   v3.new();
   const factory other() = E.new;
+//                        ^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E();
+//^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.new;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 87, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 122, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 129, 5),
-      error(diag.unusedLocalVariable, 140, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 145, 3),
-    ]);
     var element = result.findElement.unnamedConstructor('E');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1190,29 +1225,33 @@ void useConstructor() {
   }
 
   test_ConstructorElement_enum_unnamed_typeName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E] and [E.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E {
   v1,
   v2(),
   v3.new();
   const E();
   const factory E.other() = E;
+//                          ^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E();
+//^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.new;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 100, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 131, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 138, 5),
-      error(diag.unusedLocalVariable, 149, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 154, 3),
-    ]);
     var element = result.findElement.unnamedConstructor('E');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1228,29 +1267,33 @@ void useConstructor() {
   }
 
   test_ConstructorElement_enum_unnamed_typeName_explicitNew() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new E] and [E.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 enum E {
   v1,
   v2(),
   v3.new();
   const E.new();
   const factory E.other() = E.new;
+//                          ^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 void useConstructor() {
   E();
+//^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   E.new;
+//^^^^^
+// [diag.invalidReferenceToGenerativeEnumConstructorTearoff] Generative enum constructors can't be torn off.
   E a = .new();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//       ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 104, 5),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 139, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructorTearoff, 146, 5),
-      error(diag.unusedLocalVariable, 157, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 162, 3),
-    ]);
     var element = result.findElement.unnamedConstructor('E');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1266,8 +1309,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_extensionType_named_newHead() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A.foo] and [A.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 extension type A(int it) {
   new foo(this.it);
   new bar() : this.foo(0);
@@ -1277,12 +1322,10 @@ void useConstructor() {
   A.foo(0);
   A.foo;
   A a = .foo(0);
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 184, 1),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -1296,8 +1339,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_extensionType_named_primary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A.foo] and [A.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 extension type A.foo(int it) {
   new bar() : this.foo(0);
   factory baz(int it) = A.foo;
@@ -1306,12 +1351,10 @@ void useConstructor() {
   A.foo(0);
   A.foo;
   A a = .foo(0);
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 168, 1),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -1325,8 +1368,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_extensionType_named_typeName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A.foo] and [A.foo]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 extension type A(int it) {
   A.foo(this.it);
   A.bar() : this.foo(0);
@@ -1336,12 +1381,10 @@ void useConstructor() {
   A.foo(0);
   A.foo;
   A a = .foo(0);
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 182, 1),
-    ]);
     var element = result.findElement.constructor('foo');
     assertElementIndexText(result, element, r'''
 10 1:11 |.foo| IS_REFERENCED_BY qualified
@@ -1355,8 +1398,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_extensionType_unnamed_newHead() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 extension type A.named(int it) {
   new (this.it);
   new bar() : this(0);
@@ -1366,12 +1411,10 @@ void useConstructor() {
   A(0);
   A.new;
   A a = .new(0);
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 175, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1385,8 +1428,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_extensionType_unnamed_primary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 extension type A(int it) {
   new bar() : this(0);
   factory baz(int it) = A.new;
@@ -1395,12 +1440,10 @@ void useConstructor() {
   A(0);
   A.new;
   A a = .new(0);
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 152, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1414,8 +1457,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_extensionType_unnamed_typeName() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 extension type A.named(int it) {
   A(this.it);
   A.bar() : this(0);
@@ -1425,12 +1470,10 @@ void useConstructor() {
   A(0);
   A.new;
   A a = .new(0);
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 172, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1444,8 +1487,10 @@ void useConstructor() {
   }
 
   test_ConstructorElement_extensionType_unnamed_typeName_explicitNew() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [new A] and [A.new]
+//   ^^^
+// [diag.deprecatedNewInCommentReference] Using the 'new' keyword in a comment reference is deprecated.
 extension type A.named(int it) {
   A.new(this.it);
   A.bar() : this.new(0);
@@ -1455,12 +1500,10 @@ void useConstructor() {
   A.new(0);
   A.new;
   A a = .new(0);
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.deprecatedNewInCommentReference, 5, 3),
-      error(diag.unusedLocalVariable, 184, 1),
-    ]);
     var element = result.findElement.unnamedConstructor('A');
     assertElementIndexText(result, element, r'''
 10 1:11 || IS_REFERENCED_BY qualified
@@ -1474,21 +1517,22 @@ void useConstructor() {
   }
 
   test_DynamicElement() async {
-    await _indexTestUnit('''
+    await _indexTestCode('''
 dynamic f() {}
 ''');
     expect(index.usedElementOffsets, isEmpty);
   }
 
   test_EnumElement_emptyBody() async {
-    var result = await _indexTestUnit(r'''
+    await _indexTestCode(r'''
 enum E;
+//   ^
+// [diag.enumWithoutConstants] The enum must have at least one enum constant.
 ''');
-    assertErrorsInTestResult(result, [error(diag.enumWithoutConstants, 5, 1)]);
   }
 
   test_EnumElement_reference_annotation() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 enum E {
@@ -1506,7 +1550,6 @@ enum E {
 @p.E.myConstant
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.enum_('E');
     assertElementIndexText(result, element, r'''
@@ -1523,7 +1566,7 @@ Prefixes: (unprefixed),p
   }
 
   test_EnumElement_reference_comment() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 enum E { v }
@@ -1531,7 +1574,6 @@ enum E { v }
 /// [E] and [p.E].
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.enum_('E');
     assertElementIndexText(result, element, r'''
@@ -1542,7 +1584,7 @@ Prefixes: (unprefixed),p
   }
 
   test_EnumElement_reference_instanceCreation() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 enum E {
@@ -1552,13 +1594,13 @@ enum E {
 
 void f() {
   const E();
+//      ^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
   const p.E();
+//      ^^^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 75, 1),
-      error(diag.invalidReferenceToGenerativeEnumConstructor, 88, 3),
-    ]);
 
     var element = result.findElement.enum_('E');
     assertElementIndexText(result, element, r'''
@@ -1570,7 +1612,7 @@ Prefixes: (unprefixed),p
   }
 
   test_EnumElement_reference_memberAccess() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 enum E {
@@ -1583,7 +1625,6 @@ void f() {
   p.E.foo();
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.enum_('E');
     assertElementIndexText(result, element, r'''
@@ -1594,20 +1635,20 @@ Prefixes: (unprefixed),p
   }
 
   test_EnumElement_reference_namedType() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 enum E { v }
 
 void f() {
   E v1;
+//  ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v1' isn't used.
   p.E v2;
+//    ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v2' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.unusedLocalVariable, 55, 2),
-      error(diag.unusedLocalVariable, 65, 2),
-    ]);
 
     var element = result.findElement.enum_('E');
     assertElementIndexText(result, element, r'''
@@ -1618,14 +1659,13 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionElement_emptyBody() async {
-    var result = await _indexTestUnit(r'''
+    await _indexTestCode(r'''
 extension E on int;
 ''');
-    assertErrorsInTestResult(result, []);
   }
 
   test_ExtensionElement_reference_memberAccess() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension E on int {
@@ -1637,7 +1677,6 @@ void f() {
   p.E.foo();
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.extension_('E');
     assertElementIndexText(result, element, r'''
@@ -1648,7 +1687,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionElement_reference_override() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension E on int {
@@ -1660,7 +1699,6 @@ void f() {
   p.E(0).foo();
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.extension_('E');
     assertElementIndexText(result, element, r'''
@@ -1671,7 +1709,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionTypeElement_hierarchy_extensionType_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension type A(int it) {}
@@ -1679,7 +1717,6 @@ extension type A(int it) {}
 extension type B(int it) implements A {}
 extension type B_q(int it) implements p.A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.extensionType('A');
     assertElementIndexText(result, element, r'''
@@ -1692,7 +1729,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionTypeElement_reference_annotation() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension type const A(int it) {}
@@ -1701,7 +1738,6 @@ extension type const A(int it) {}
 @p.A(0)
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.extensionType('A');
     assertElementIndexText(result, element, r'''
@@ -1712,7 +1748,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionTypeElement_reference_comment() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension type A(int it) {}
@@ -1720,7 +1756,6 @@ extension type A(int it) {}
 /// [A] and [p.A].
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.extensionType('A');
     assertElementIndexText(result, element, r'''
@@ -1731,7 +1766,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionTypeElement_reference_instanceCreation() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension type A(int it) {}
@@ -1741,7 +1776,6 @@ void f() {
   p.A(0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.extensionType('A');
     assertElementIndexText(result, element, r'''
@@ -1752,7 +1786,7 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionTypeElement_reference_memberAccess() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension type A(int it) {
@@ -1764,7 +1798,6 @@ void f() {
   p.A.foo();
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.extensionType('A');
     assertElementIndexText(result, element, r'''
@@ -1775,20 +1808,20 @@ Prefixes: (unprefixed),p
   }
 
   test_ExtensionTypeElement_reference_namedType() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 extension type A(int it) {}
 
 void f() {
   A v1;
+//  ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v1' isn't used.
   p.A v2;
+//    ^^
+// [diag.unusedLocalVariable] The value of the local variable 'v2' isn't used.
 }
 ''');
-    assertErrorsInTestResult(result, [
-      error(diag.unusedLocalVariable, 70, 2),
-      error(diag.unusedLocalVariable, 80, 2),
-    ]);
 
     var element = result.findElement.extensionType('A');
     assertElementIndexText(result, element, r'''
@@ -1799,11 +1832,13 @@ Prefixes: (unprefixed),p
   }
 
   test_FieldElement_ofClass_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 class A {
   int foo;
   A({this.foo});
+//        ^^^
+// [diag.missingDefaultValueForParameter] The parameter 'foo' can't have a value of 'null' because of its type, but the implicit default value is 'null'.
   A.foo() : foo = 0;
 
   void useField() {
@@ -1843,9 +1878,11 @@ void useField(A a) {
   }
 
   test_FieldElement_ofClass_instance_synthetic_hasGetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A() : foo = 0;
+//      ^^^^^^^
+// [diag.initializerForNonExistentField] 'foo' isn't a field in the enclosing class.
   int get foo => 0;
 }
 ''');
@@ -1856,9 +1893,11 @@ class A {
   }
 
   test_FieldElement_ofClass_instance_synthetic_hasGetterSetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A() : foo = 0;
+//      ^^^^^^^
+// [diag.initializerForNonExistentField] 'foo' isn't a field in the enclosing class.
   int get foo => 0;
   set foo(_) {}
 }
@@ -1870,9 +1909,11 @@ class A {
   }
 
   test_FieldElement_ofClass_instance_synthetic_hasSetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A() : foo = 0;
+//      ^^^^^^^
+// [diag.initializerForNonExistentField] 'foo' isn't a field in the enclosing class.
   set foo(_) {}
 }
 ''');
@@ -1883,7 +1924,7 @@ class A {
   }
 
   test_FieldElement_ofClass_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 class A {
   static int foo = 0;
@@ -1899,6 +1940,10 @@ void useField() {
   A.foo;
   A.foo = 0;
   A a = .foo;
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
+//      ^^^^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'A'.
 }
 ''');
 
@@ -1921,11 +1966,13 @@ void useField() {
   }
 
   test_FieldElement_ofEnum_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [E.foo]
 enum E {
   v;
   int? foo; // a compile-time error
+//     ^^^
+// [diag.nonFinalFieldInEnum] Enums can only declare final fields.
   E({this.foo});
   void useField() {
     foo;
@@ -1936,6 +1983,8 @@ void useField(E e) {
   e.foo;
   e.foo = 0;
   E(foo: 0);
+//^
+// [diag.invalidReferenceToGenerativeEnumConstructor] Generative enum constructors can only be used to create an enum constant.
 }
 ''');
     var field = result.findElement.field('foo');
@@ -1960,7 +2009,7 @@ void useField(E e) {
   }
 
   test_FieldElement_ofEnum_instance_index() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 enum MyEnum {
   v1, v2, v3
 }
@@ -1979,10 +2028,12 @@ void f() {
   }
 
   test_FieldElement_ofEnum_instance_synthetic_hasGetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 enum E {
   v;
   E() : foo = 0;
+//      ^^^^^^^
+// [diag.initializerForNonExistentField] 'foo' isn't a field in the enclosing class.
   int get foo => 0;
 }
 ''');
@@ -1993,10 +2044,12 @@ enum E {
   }
 
   test_FieldElement_ofEnum_instance_synthetic_hasGetterSetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 enum E {
   v;
   E() : foo = 0;
+//      ^^^^^^^
+// [diag.initializerForNonExistentField] 'foo' isn't a field in the enclosing class.
   int get foo => 0;
   set foo(_) {}
 }
@@ -2008,10 +2061,12 @@ enum E {
   }
 
   test_FieldElement_ofEnum_instance_synthetic_hasSetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 enum E {
   v;
   E() : foo = 0;
+//      ^^^^^^^
+// [diag.initializerForNonExistentField] 'foo' isn't a field in the enclosing class.
   set foo(_) {}
 }
 ''');
@@ -2022,7 +2077,7 @@ enum E {
   }
 
   test_FieldElement_ofEnum_static_constants() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 /// [v1], [MyEnum.v1], and [p.MyEnum.v1]
@@ -2059,7 +2114,7 @@ void f() {
   }
 
   test_FieldElement_ofExtensionType_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 extension type A(int it) {
   static int foo = 0;
@@ -2091,9 +2146,11 @@ void useField() {
   }
 
   test_fieldFormalParameter_noSuchField() async {
-    await _indexTestUnit('''
+    await _indexTestCode('''
 class B<T> {
   B({this.x}) {}
+//   ^^^^^^
+// [diag.initializingFormalForNonExistentField] 'x' isn't a field in the enclosing class.
 
   foo() {
     B<int>(x: 1);
@@ -2104,7 +2161,7 @@ class B<T> {
   }
 
   test_FieldFormalParameterElement_ofConstructor_optionalNamed_dotShorthand() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A({this.test}) : assert(test != null);
   int? test;
@@ -2113,7 +2170,6 @@ void foo() {
   A _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.fieldFormalParameter('test');
     assertElementIndexText(result, element, r'''
 36 2:27 |test| IS_READ_BY
@@ -2128,20 +2184,21 @@ void foo<T>({T? test}) {}
     newFile('$testPackageLibPath/b.dart', r'''
 void foo<T>({T? test}) {}
 ''');
-    var result = await _indexTestUnit(r"""
+    await _indexTestCode(r"""
 import 'a.dart';
 import 'b.dart';
 
 void f() {
   foo(test: 0);
+//^^^
+// [diag.ambiguousImport] The name 'foo' is defined in the libraries 'package:test/a.dart' and 'package:test/b.dart'.
 }
 """);
     // No exceptions.
-    assertErrorsInTestResult(result, [error(diag.ambiguousImport, 48, 3)]);
   }
 
   test_FormalParameterElement_ofConstructor_primary_optionalNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A({int? test}) {
   /// [test]
   this : assert(test != null) {
@@ -2168,7 +2225,6 @@ void f() {
   A _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 30 2:8 |test| IS_REFERENCED_BY
@@ -2187,7 +2243,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_primary_optionalNamed_genericClass() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A<T>({T? test}) {
   /// [test]
   this : assert(test != null) {
@@ -2213,7 +2269,6 @@ void f() {
   A<int> _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 31 2:8 |test| IS_REFERENCED_BY
@@ -2231,7 +2286,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_primary_optionalPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A([int? test]) {
   /// [test]
   this : assert(test != null) {
@@ -2258,7 +2313,6 @@ void f() {
   A _ = .new(0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 30 2:8 |test| IS_REFERENCED_BY
@@ -2273,7 +2327,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_primary_requiredNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A({required int test}) {
   /// [test]
   this : assert(test != -1) {
@@ -2300,7 +2354,6 @@ void f() {
   A _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 38 2:8 |test| IS_REFERENCED_BY
@@ -2319,7 +2372,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_primary_requiredPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A(int test) {
   /// [test]
   this : assert(test != -1) {
@@ -2346,7 +2399,6 @@ void f() {
   A _ = .new(0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 27 2:8 |test| IS_REFERENCED_BY
@@ -2361,7 +2413,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_typeName_optionalNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   A({int? test}) : assert(test != null) {
@@ -2388,7 +2440,6 @@ void f() {
   A _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2407,7 +2458,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_typeName_optionalNamed_genericClass() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A<T> {
   /// [test]
   A({T? test}) : assert(test != null) {
@@ -2433,7 +2484,6 @@ void f() {
   A<int> _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 20 2:8 |test| IS_REFERENCED_BY
@@ -2451,7 +2501,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_typeName_optionalPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   A([int? test]) : assert(test != null) {
@@ -2478,7 +2528,6 @@ void f() {
   A _ = .new(0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2493,7 +2542,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_typeName_requiredNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   A({required int test}) : assert(test != -1) {
@@ -2520,7 +2569,6 @@ void f() {
   A _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2539,7 +2587,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofConstructor_typeName_requiredPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   A(int test) : assert(test != -1) {
@@ -2566,7 +2614,6 @@ void f() {
   A _ = .new(0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('A').parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2581,7 +2628,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofGenericFunctionType_optionalNamed() async {
-    var result = await _indexTestUnit('''
+    await _indexTestCode('''
 typedef F = void Function({int? test});
 
 void g(F f) {
@@ -2590,11 +2637,10 @@ void g(F f) {
 ''');
     // We should not crash because of reference to "test" - a named parameter
     // of a generic function type.
-    assertErrorsInTestResult(result, []);
   }
 
   test_FormalParameterElement_ofGenericFunctionType_optionalNamed_call() async {
-    var result = await _indexTestUnit('''
+    await _indexTestCode('''
 typedef F<T> = void Function({T? test});
 
 void g(F<int> f) {
@@ -2602,11 +2648,10 @@ void g(F<int> f) {
 }
 ''');
     // No exceptions.
-    assertErrorsInTestResult(result, []);
   }
 
   test_FormalParameterElement_ofLocalFunction_optionalNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 void f() {
   /// [test]
   void foo({int? test}) {
@@ -2622,14 +2667,13 @@ void f() {
   (foo)(test: 2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 ''');
   }
 
   test_FormalParameterElement_ofLocalFunction_optionalPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 void f() {
   /// [test]
   void foo([int? test]) {
@@ -2645,14 +2689,13 @@ void f() {
   (foo)(2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 ''');
   }
 
   test_FormalParameterElement_ofLocalFunction_requiredNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 void f() {
   /// [test]
   void foo({required int test}) {
@@ -2668,14 +2711,13 @@ void f() {
   (foo)(test: 2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 ''');
   }
 
   test_FormalParameterElement_ofLocalFunction_requiredPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 void f() {
   /// [test]
   void foo(int test) {
@@ -2691,14 +2733,13 @@ void f() {
   (foo)(2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 ''');
   }
 
   test_FormalParameterElement_ofMethod_optionalNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   void foo({int? test}) {
@@ -2716,7 +2757,6 @@ void f(A a) {
   (a.foo)(test: 2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2732,7 +2772,7 @@ void f(A a) {
   }
 
   test_FormalParameterElement_ofMethod_optionalNamed_genericClass() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A<T> {
   /// [test]
   void foo({T? test}) {
@@ -2750,7 +2790,6 @@ void f(A<int> a) {
   (a.foo)(test: 2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 20 2:8 |test| IS_REFERENCED_BY
@@ -2765,7 +2804,7 @@ void f(A<int> a) {
   }
 
   test_FormalParameterElement_ofMethod_optionalPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   void foo([int? test]) {
@@ -2783,7 +2822,6 @@ void f(A a) {
   (a.foo)(2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2796,7 +2834,7 @@ void f(A a) {
   }
 
   test_FormalParameterElement_ofMethod_requiredNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   void foo({required int test}) {
@@ -2814,7 +2852,6 @@ void f(A a) {
   (a.foo)(test: 2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2830,7 +2867,7 @@ void f(A a) {
   }
 
   test_FormalParameterElement_ofMethod_requiredPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   /// [test]
   void foo(int test) {
@@ -2848,7 +2885,6 @@ void f(A a) {
   (a.foo)(2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 17 2:8 |test| IS_REFERENCED_BY
@@ -2861,7 +2897,7 @@ void f(A a) {
   }
 
   test_FormalParameterElement_ofTopLevelFunction_optionalNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [test]
 void foo({int? test}) {
   test;
@@ -2876,7 +2912,6 @@ void f() {
   (foo)(test: 2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 5 1:6 |test| IS_REFERENCED_BY
@@ -2892,7 +2927,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofTopLevelFunction_optionalNamed_argumentAnywhere() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [test]
 void foo(int a, int b, {int? test}) {
   test;
@@ -2908,7 +2943,6 @@ void f() {
   (foo)(0, test: 2, 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 5 1:6 |test| IS_REFERENCED_BY
@@ -2924,7 +2958,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofTopLevelFunction_optionalPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [test]
 void foo([int? test]) {
   test;
@@ -2939,7 +2973,6 @@ void f() {
   (foo)(2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 5 1:6 |test| IS_REFERENCED_BY
@@ -2952,7 +2985,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofTopLevelFunction_requiredNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [test]
 void foo({required int test}) {
   test;
@@ -2968,7 +3001,6 @@ void f() {
   (foo)(test: 2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 5 1:6 |test| IS_REFERENCED_BY
@@ -2984,7 +3016,7 @@ void f() {
   }
 
   test_FormalParameterElement_ofTopLevelFunction_requiredPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [test]
 void foo(int test) {
   test;
@@ -3000,7 +3032,6 @@ void f() {
   (foo)(2);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.parameter('test');
     assertElementIndexText(result, element, r'''
 5 1:6 |test| IS_REFERENCED_BY
@@ -3013,7 +3044,7 @@ void f() {
   }
 
   test_FormalParameterElement_synthetic_leastUpperBound() async {
-    var result = await _indexTestUnit('''
+    await _indexTestCode('''
 int f1({int? test}) => 0;
 int f2({int? test}) => 0;
 void g(bool b) {
@@ -3022,11 +3053,10 @@ void g(bool b) {
 }''');
     // We should not crash because of reference to "test" - a named parameter
     // of a synthetic LUB FunctionElement created for "f".
-    assertErrorsInTestResult(result, []);
   }
 
   test_GetterElement_ofClass_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 class A {
   int get foo => 0;
@@ -3051,7 +3081,7 @@ void useGetter(A a) {
   }
 
   test_GetterElement_ofClass_invocation() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   get foo => null;
   void useGetter() {
@@ -3067,7 +3097,7 @@ class A {
   }
 
   test_GetterElement_ofClass_objectPattern() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   int get foo => 0;
 }
@@ -3075,6 +3105,8 @@ class A {
 void useGetter(Object? x) {
   if (x case A(foo: 0)) {}
   if (x case A(: var foo)) {}
+//                   ^^^
+// [diag.unusedLocalVariable] The value of the local variable 'foo' isn't used.
 }
 ''');
     var element = result.findElement.getter('foo');
@@ -3085,7 +3117,7 @@ void useGetter(Object? x) {
   }
 
   test_GetterElement_ofClass_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'test.dart' as p;
 
 /// [foo], [A.foo], [p.A.foo]
@@ -3114,7 +3146,7 @@ void useGetter() {
 
   test_LibraryFragment_reference_export() async {
     newFile('$testPackageLibPath/lib.dart', '');
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 export 'lib.dart';
 ''');
     var export = result.findElement.export('package:test/lib.dart');
@@ -3126,8 +3158,10 @@ export 'lib.dart';
 
   test_LibraryFragment_reference_import() async {
     newFile('$testPackageLibPath/lib.dart', '');
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'lib.dart';
+//     ^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'lib.dart'.
 ''');
     var import = result.findElement.import('package:test/lib.dart');
     var fragment = import.importedLibrary!.firstFragment;
@@ -3138,7 +3172,7 @@ import 'lib.dart';
 
   test_LibraryFragment_reference_part() async {
     newFile('$testPackageLibPath/my_unit.dart', "part of 'test.dart';");
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 part 'my_unit.dart';
 ''');
     var fragment = result.findElement.part('package:test/my_unit.dart');
@@ -3155,14 +3189,16 @@ part of 'b.dart';
 library lib;
 part 'a.dart';
 ''');
-    await _indexTestUnit('''
+    await _indexTestCode('''
 part 'b.dart';
+//   ^^^^^^^^
+// [diag.partOfNonPart] The included part 'package:test/b.dart' must have a part-of directive.
 ''');
     // No exception, even though a.dart is a part of b.dart part.
   }
 
   test_MethodElement_normal_ofClass_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 class A {
   void foo() {}
@@ -3173,6 +3209,8 @@ class A {
     foo;
     if (x case A(foo: _)) {}
     if (x case A(: var foo)) {}
+//                     ^^^
+// [diag.unusedLocalVariable] The value of the local variable 'foo' isn't used.
   }
 }
 void useFoo(A a) {
@@ -3196,7 +3234,7 @@ void useFoo(A a) {
   }
 
   test_MethodElement_normal_ofClass_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'test.dart' as p;
 
 /// [foo], [A.foo], [p.A.foo]
@@ -3212,6 +3250,8 @@ void useFoo() {
   A.foo();
   A.foo;
   A a = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'a' isn't used.
   p.A.foo();
   p.A.foo;
 }
@@ -3232,7 +3272,7 @@ void useFoo() {
   }
 
   test_MethodElement_normal_ofEnum_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [E.foo]
 enum E {
   v;
@@ -3263,7 +3303,7 @@ void useFoo(E e) {
   }
 
   test_MethodElement_normal_ofEnum_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [E.foo]
 enum E {
   v;
@@ -3290,7 +3330,7 @@ void useFoo() {
   }
 
   test_MethodElement_normal_ofExtension_named_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [E.foo]
 extension E on int {
   void foo() {}
@@ -3311,7 +3351,7 @@ void useFoo() {
   }
 
   test_MethodElement_normal_ofExtension_named_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [E.foo]
 extension E on int {
   static void foo() {}
@@ -3332,7 +3372,7 @@ void useFoo() {
   }
 
   test_MethodElement_normal_ofExtension_unnamed_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [int.foo]
 extension on int {
   void foo() {} // int
@@ -3367,7 +3407,7 @@ void useFoo() {
   }
 
   test_MethodElement_normal_ofExtensionType_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 extension type A(int it) {
   void foo() {}
@@ -3398,7 +3438,7 @@ void useFoo() {
   }
 
   test_MethodElement_normal_ofExtensionType_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 extension type A(int it) {
   static void foo() {}
@@ -3424,7 +3464,7 @@ void useFoo() {
   }
 
   test_MethodElement_normal_ofMixin_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [M.foo]
 mixin M {
   void foo() {}
@@ -3454,7 +3494,7 @@ void useFoo(M m) {
   }
 
   test_MethodElement_normal_ofMixin_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [M.foo]
 mixin M {
   static void foo() {}
@@ -3467,6 +3507,10 @@ void useFoo() {
   M.foo();
   M.foo;
   M m = .foo();
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'm' isn't used.
+//      ^^^^^^
+// [diag.useOfVoidResult] This expression has a type of 'void' so its value can't be used.
 }
 ''');
     var element = result.findElement.method('foo');
@@ -3482,7 +3526,7 @@ void useFoo() {
   }
 
   test_MethodElement_operator_ofClass_binary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator +] and [A.operator +]
 class A {
   operator +(other) => this;
@@ -3506,7 +3550,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofClass_index() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []] and [A.operator []]
 class A {
   operator [](i) => null;
@@ -3522,7 +3566,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofClass_indexEq() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []=] and [A.operator []=]
 class A {
   operator []=(i, v) {}
@@ -3538,7 +3582,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofClass_prefix() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator ~] and [A.operator ~]
 class A {
   A operator ~() => this;
@@ -3556,7 +3600,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofEnum_binary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator +] and [E.operator +]
 enum E {
   v;
@@ -3565,8 +3609,14 @@ enum E {
 void useOperator(E e) {
   e + 1;
   e += 2;
+//     ^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'E'.
   ++e;
+//^^^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'E'.
   e++;
+//^^^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'E'.
 }
 ''');
     var element = result.findElement.method('+');
@@ -3581,7 +3631,7 @@ void useOperator(E e) {
   }
 
   test_MethodElement_operator_ofEnum_index() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []] and [E.operator []]
 enum E {
   v;
@@ -3598,7 +3648,7 @@ void useOperator(E e) {
   }
 
   test_MethodElement_operator_ofEnum_indexEq() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []=] and [E.operator []=]
 enum E {
   v;
@@ -3615,7 +3665,7 @@ void useOperator(E e) {
   }
 
   test_MethodElement_operator_ofEnum_prefix() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator ~] and [E.operator ~]
 enum E {
   e;
@@ -3634,7 +3684,7 @@ void useOperator(E e) {
   }
 
   test_MethodElement_operator_ofExtension_binary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator +] and [E.operator +]
 extension E on int {
   int operator +(int other) => 0;
@@ -3652,7 +3702,7 @@ void useOperator(int e) {
   }
 
   test_MethodElement_operator_ofExtension_index() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []] and [E.operator []]
 extension E on int {
   int operator [](int index) => 0;
@@ -3668,7 +3718,7 @@ void useOperator(int e) {
   }
 
   test_MethodElement_operator_ofExtension_indexEq() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []=] and [E.operator []=]
 extension E on int {
   operator []=(int index, int value) {}
@@ -3684,7 +3734,7 @@ void useOperator(int e) {
   }
 
   test_MethodElement_operator_ofExtension_prefix() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator ~] and [E.operator ~]
 extension E on int {
   int operator ~() => 0;
@@ -3702,7 +3752,7 @@ void useOperator(int e) {
   }
 
   test_MethodElement_operator_ofExtensionType_binary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator +] and [A.operator +]
 extension type A(int it) {
   int operator +(int other) => 0;
@@ -3710,8 +3760,14 @@ extension type A(int it) {
 void useOperator(A a) {
   a + 1;
   a += 2;
+//     ^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'A'.
   ++a;
+//^^^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'A'.
   a++;
+//^^^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'A'.
 }
 ''');
     var element = result.findElement.method('+');
@@ -3726,7 +3782,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofExtensionType_index() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []] and [A.operator []]
 extension type A(int it) {
   int operator [](int index) => 0;
@@ -3742,7 +3798,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofExtensionType_indexEq() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []=] and [A.operator []=]
 extension type A(int it) {
   operator []=(int index, int value) {}
@@ -3758,7 +3814,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofExtensionType_prefix() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator ~] and [A.operator ~]
 extension type A(int it) {
   int operator ~() => 0;
@@ -3776,7 +3832,7 @@ void useOperator(A a) {
   }
 
   test_MethodElement_operator_ofMixin_binary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator +] and [M.operator +]
 mixin M {
   int operator +(int other) => 0;
@@ -3784,8 +3840,14 @@ mixin M {
 void useOperator(M m) {
   m + 1;
   m += 2;
+//     ^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'M'.
   ++m;
+//^^^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'M'.
   m++;
+//^^^
+// [diag.invalidAssignment] A value of type 'int' can't be assigned to a variable of type 'M'.
 }
 ''');
     var element = result.findElement.method('+');
@@ -3800,7 +3862,7 @@ void useOperator(M m) {
   }
 
   test_MethodElement_operator_ofMixin_index() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []] and [M.operator []]
 mixin M {
   int operator [](int index) => 0;
@@ -3816,7 +3878,7 @@ void useOperator(M m) {
   }
 
   test_MethodElement_operator_ofMixin_indexEq() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator []=] and [M.operator []=]
 mixin M {
   operator []=(int index, int value) {}
@@ -3832,7 +3894,7 @@ void useOperator(M m) {
   }
 
   test_MethodElement_operator_ofMixin_prefix() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [operator ~] and [M.operator ~]
 mixin M {
   int operator ~() => 0;
@@ -3850,18 +3912,16 @@ void useOperator(M m) {
   }
 
   test_MixinElement_emptyBody() async {
-    var result = await _indexTestUnit(r'''
+    await _indexTestCode(r'''
 mixin M;
 ''');
-    assertErrorsInTestResult(result, []);
   }
 
   test_MixinElement_hierarchy_class_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 class B implements A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3871,11 +3931,10 @@ class B implements A {}
   }
 
   test_MixinElement_hierarchy_class_with() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 class B extends Object with A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3885,11 +3944,10 @@ class B extends Object with A {}
   }
 
   test_MixinElement_hierarchy_classTypeAlias_with() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 class B = Object with A;
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3899,13 +3957,12 @@ class B = Object with A;
   }
 
   test_MixinElement_hierarchy_enum_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 enum E implements A {
   v
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3915,13 +3972,12 @@ enum E implements A {
   }
 
   test_MixinElement_hierarchy_enum_with() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 enum E with A {
   v
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3931,11 +3987,10 @@ enum E with A {
   }
 
   test_MixinElement_hierarchy_extensionType_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 extension type E(A it) implements A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3946,11 +4001,10 @@ extension type E(A it) implements A {}
   }
 
   test_MixinElement_hierarchy_mixin_implements() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 mixin M implements A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3960,11 +4014,10 @@ mixin M implements A {}
   }
 
   test_MixinElement_hierarchy_mixin_on() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 mixin A {}
 mixin M on A {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3974,7 +4027,7 @@ mixin M on A {}
   }
 
   test_MixinElement_reference_annotation() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 mixin A {
@@ -3985,7 +4038,6 @@ mixin A {
 @p.A.myConstant
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -3996,7 +4048,7 @@ Prefixes: (unprefixed),p
   }
 
   test_MixinElement_reference_comment() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 mixin A {}
@@ -4004,7 +4056,6 @@ mixin A {}
 /// [A] and [p.A].
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -4015,7 +4066,7 @@ Prefixes: (unprefixed),p
   }
 
   test_MixinElement_reference_memberAccess() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 mixin A {
@@ -4027,7 +4078,6 @@ void f() {
   p.A.foo();
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -4038,14 +4088,13 @@ Prefixes: (unprefixed),p
   }
 
   test_MixinElement_reference_namedType() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 mixin A {}
 
 void f(A v1, p.A v2) {}
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.mixin('A');
     assertElementIndexText(result, element, r'''
@@ -4058,22 +4107,25 @@ Prefixes: (unprefixed),p
   test_MultiplyDefinedElement() async {
     newFile('$testPackageLibPath/a1.dart', 'class A {}');
     newFile('$testPackageLibPath/a2.dart', 'class A {}');
-    await _indexTestUnit('''
+    await _indexTestCode('''
 import 'a1.dart';
 import 'a2.dart';
 A v = null;
+// [diag.ambiguousImport][column 1][length 1] The name 'A' is defined in the libraries 'package:test/a1.dart' and 'package:test/a2.dart'.
 ''');
   }
 
   test_NeverElement() async {
-    await _indexTestUnit('''
+    await _indexTestCode('''
 Never f() {}
+//    ^
+// [diag.bodyMightCompleteNormally] The body might complete normally, causing 'null' to be returned, but the return type, 'Never', is a potentially non-nullable type.
 ''');
     expect(index.usedElementOffsets, isEmpty);
   }
 
   test_SetterElement_ofClass_instance() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 /// [foo] and [A.foo]
 class A {
   set foo(int _) {}
@@ -4098,7 +4150,7 @@ void useSetter(A a) {
   }
 
   test_SetterElement_ofClass_static() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'test.dart' as p;
 
 /// [foo], [A.foo], [p.A.foo]
@@ -4134,23 +4186,37 @@ class D {}
 class E {}
 ''');
     String libP = '${libFile.path};${libFile.path}';
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'lib.dart';
 
 class X extends A {
   X();
+//^
+// [diag.notInitializedNonNullableInstanceFieldConstructor] Non-nullable instance field 'field1' must be initialized.
+// [diag.notInitializedNonNullableInstanceFieldConstructor] Non-nullable instance field 'field2' must be initialized.
   X.namedConstructor();
+//^^^^^^^^^^^^^^^^^^
+// [diag.notInitializedNonNullableInstanceFieldConstructor] Non-nullable instance field 'field1' must be initialized.
+// [diag.notInitializedNonNullableInstanceFieldConstructor] Non-nullable instance field 'field2' must be initialized.
 
   int field1, field2;
   int get getter1 => null;
+//                   ^^^^
+// [diag.returnOfInvalidTypeFromFunction] A value of type 'Null' can't be returned from the function 'getter1' because it has a return type of 'int'.
   void set setter1(_) {}
   void method1() {}
 
   static int staticField;
+//           ^^^^^^^^^^^
+// [diag.notInitializedNonNullableVariable] The non-nullable variable 'staticField' must be initialized.
   static void staticMethod() {}
 }
 
 class Y extends Object with B, C {
+//                          ^
+// [diag.classUsedAsMixin] The class 'B' can't be used as a mixin because it's neither a mixin class nor a mixin.
+//                             ^
+// [diag.classUsedAsMixin] The class 'C' can't be used as a mixin because it's neither a mixin class nor a mixin.
   void methodY() {}
 }
 
@@ -4186,11 +4252,17 @@ class C {}
 class D {}
 ''');
     String libP = '${libFile.path};${libFile.path}';
-    await _indexTestUnit('''
+    await _indexTestCode('''
 import 'lib.dart';
 
 class X = A with B, C;
+//               ^
+// [diag.classUsedAsMixin] The class 'B' can't be used as a mixin because it's neither a mixin class nor a mixin.
+//                  ^
+// [diag.classUsedAsMixin] The class 'C' can't be used as a mixin because it's neither a mixin class nor a mixin.
 class Y = A with B implements C, D;
+//               ^
+// [diag.classUsedAsMixin] The class 'B' can't be used as a mixin because it's neither a mixin class nor a mixin.
 ''');
 
     expect(index.supertypes, hasLength(7));
@@ -4206,8 +4278,10 @@ class Y = A with B implements C, D;
   }
 
   test_subtypes_dynamic() async {
-    await _indexTestUnit('''
+    await _indexTestCode('''
 class X extends dynamic {
+//              ^^^^^^^
+// [diag.extendsNonClass] Classes can only extend other classes.
   void foo() {}
 }
 ''');
@@ -4218,7 +4292,7 @@ class X extends dynamic {
 
   test_subtypes_enum_implements() async {
     String libP = '${testFile.path};${testFile.path}';
-    await _indexTestUnit('''
+    await _indexTestCode('''
 class A {}
 
 enum E implements A {
@@ -4233,7 +4307,7 @@ enum E implements A {
 
   test_subtypes_enum_with() async {
     String libP = '${testFile.path};${testFile.path}';
-    await _indexTestUnit('''
+    await _indexTestCode('''
 mixin M {}
 
 enum E with M {
@@ -4254,7 +4328,7 @@ class A {
 }
 ''');
     String libP = '${libFile.path};${libFile.path}';
-    await _indexTestUnit('''
+    await _indexTestCode('''
 import 'lib.dart';
 
 extension type X(A it) implements A {
@@ -4277,7 +4351,7 @@ extension type A(int it) {
 }
 ''');
     String libP = '${libFile.path};${libFile.path}';
-    await _indexTestUnit('''
+    await _indexTestCode('''
 import 'lib.dart';
 
 extension type X(int it) implements A {
@@ -4301,7 +4375,7 @@ class D {}
 class E {}
 ''');
     String libP = '${libFile.path};${libFile.path}';
-    await _indexTestUnit('''
+    await _indexTestCode('''
 import 'lib.dart';
 
 mixin X on A implements B, C {}
@@ -4320,7 +4394,7 @@ mixin Y on A, B implements C;
   }
 
   test_SuperFormalParameterElement_ofConstructor_optionalNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A({int? test});
 }
@@ -4335,7 +4409,6 @@ void f() {
   B _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('B').parameter('test');
     assertElementIndexText(result, element, r'''
 58 6:8 |test| IS_REFERENCED_BY
@@ -4346,7 +4419,7 @@ void f() {
   }
 
   test_SuperFormalParameterElement_ofConstructor_optionalPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A([int? test]);
 }
@@ -4361,7 +4434,6 @@ void f() {
   B _ = .new(0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('B').parameter('test');
     assertElementIndexText(result, element, r'''
 58 6:8 |test| IS_REFERENCED_BY
@@ -4370,7 +4442,7 @@ void f() {
   }
 
   test_SuperFormalParameterElement_ofConstructor_requiredNamed() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A({required int test});
 }
@@ -4385,7 +4457,6 @@ void f() {
   B _ = .new(test: 0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('B').parameter('test');
     assertElementIndexText(result, element, r'''
 66 6:8 |test| IS_REFERENCED_BY
@@ -4396,7 +4467,7 @@ void f() {
   }
 
   test_SuperFormalParameterElement_ofConstructor_requiredPositional() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A {
   A(int test);
 }
@@ -4411,7 +4482,6 @@ void f() {
   B _ = .new(0);
 }
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.unnamedConstructor('B').parameter('test');
     assertElementIndexText(result, element, r'''
 55 6:8 |test| IS_REFERENCED_BY
@@ -4420,7 +4490,7 @@ void f() {
   }
 
   test_TopLevelFunctionElement() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 void foo() {}
@@ -4433,7 +4503,6 @@ void f() {
   p.foo;
 }
 ''');
-    assertErrorsInTestResult(result, []);
 
     var element = result.findElement.topFunction('foo');
     assertElementIndexText(result, element, r'''
@@ -4448,8 +4517,10 @@ Prefixes: (unprefixed),p
   }
 
   test_TopLevelFunctionElement_loadLibrary() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'dart:math' deferred as math;
+//     ^^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'dart:math'.
 
 void f() {
   math.loadLibrary();
@@ -4463,14 +4534,16 @@ void f() {
   }
 
   test_TopLevelVariableElement_reference() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'test.dart' as p;
 
 var foo = 0;
 
 /// [foo] and [p.foo].
 @foo
+// [diag.invalidAnnotation][column 1][length 4] Annotation must be either a const variable reference or const constructor invocation.
 @p.foo
+// [diag.invalidAnnotation][column 1][length 6] Annotation must be either a const variable reference or const constructor invocation.
 void f() {
   foo;
   foo = 0;
@@ -4500,8 +4573,10 @@ Prefixes: (unprefixed),p
   }
 
   test_TopLevelVariableElement_reference_combinator_show_hasGetterSetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'test.dart' show foo;
+//     ^^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'test.dart'.
 
 int get foo => 0;
 void set foo(_) {}
@@ -4513,8 +4588,10 @@ void set foo(_) {}
   }
 
   test_TopLevelVariableElement_reference_combinator_show_hasSetter() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 import 'test.dart' show foo;
+//     ^^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'test.dart'.
 
 void set foo(_) {}
 ''');
@@ -4525,7 +4602,7 @@ void set foo(_) {}
   }
 
   test_TypeAliasElement_legacy_reference() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 typedef void A();
 /// [A]
 void f(A p) {}
@@ -4538,7 +4615,7 @@ void f(A p) {}
   }
 
   test_TypeAliasElement_modern_hierarchy_class_extends() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A<T> {}
 typedef B = A<int>;
 class C extends B {}
@@ -4556,7 +4633,7 @@ class C extends B {}
   }
 
   test_TypeAliasElement_modern_hierarchy_class_implements() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A<T> {}
 typedef B = A<int>;
 class C implements B {}
@@ -4574,10 +4651,12 @@ class C implements B {}
   }
 
   test_TypeAliasElement_modern_hierarchy_class_with() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A<T> {}
 typedef B = A<int>;
 class C extends Object with B {}
+//                          ^
+// [diag.classUsedAsMixin] The class 'A' can't be used as a mixin because it's neither a mixin class nor a mixin.
 ''');
     var element = result.findElement.typeAlias('B');
     assertElementIndexText(result, element, r'''
@@ -4592,7 +4671,7 @@ class C extends Object with B {}
   }
 
   test_TypeAliasElement_modern_reference() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class A<T> {
   static int field = 0;
   static void method() {}
@@ -4603,6 +4682,8 @@ typedef B = A<int>;
 /// [B]
 void f(B p) {
   B v;
+//  ^
+// [diag.unusedLocalVariable] The value of the local variable 'v' isn't used.
   B();
   B.field;
   B.field = 0;
@@ -4627,7 +4708,7 @@ void f(B p) {
   }
 
   test_TypeAliasElement_modern_reference_comment() async {
-    var result = await _indexTestUnit(r'''
+    var result = await _indexTestCode(r'''
 import 'test.dart' as p;
 
 class A<T> {}
@@ -4636,7 +4717,6 @@ typedef B = A<int>;
 /// [B] and [p.B].
 void f() {}
 ''');
-    assertErrorsInTestResult(result, []);
     var element = result.findElement.typeAlias('B');
     assertElementIndexText(result, element, r'''
 66 6:6 |B| IS_REFERENCED_BY
@@ -4651,7 +4731,7 @@ Prefixes: (unprefixed),p
   }
 
   test_usedName_inLibraryIdentifier() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 library aaa.bbb.ccc;
 class C {
   var bbb;
@@ -4666,7 +4746,7 @@ void f(p) {
   }
 
   test_usedName_qualified_resolved() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class C {
   var x;
 }
@@ -4685,7 +4765,7 @@ void f(C c) {
   }
 
   test_usedName_qualified_unresolved() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 void f(p) {
   p.x;
   p.x = 1;
@@ -4701,7 +4781,7 @@ void f(p) {
   }
 
   test_usedName_unqualified_resolved() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 class C {
   var x;
   m() {
@@ -4720,12 +4800,20 @@ class C {
   }
 
   test_usedName_unqualified_unresolved() async {
-    var result = await _indexTestUnit('''
+    var result = await _indexTestCode('''
 void f() {
   x;
+//^
+// [diag.undefinedIdentifier] Undefined name 'x'.
   x = 1;
+//^
+// [diag.undefinedIdentifier] Undefined name 'x'.
   x += 2;
+//^
+// [diag.undefinedIdentifier] Undefined name 'x'.
   x();
+//^
+// [diag.undefinedFunction] The function 'x' isn't defined.
 }
 ''');
     assertThatName(result, 'x')
@@ -4966,12 +5054,15 @@ mixin _IndexMixin on PubPackageResolutionTest {
     return index.getLibraryFragmentId(unitElement);
   }
 
-  Future<TestResolvedUnitResult> _indexTestUnit(String code) async {
-    var result = await resolveTestCode(code);
-
+  void _indexResult(TestResolvedUnitResult result) {
     var indexBuilder = indexUnit(result.unit);
     var indexBytes = indexBuilder.toBuffer();
     index = AnalysisDriverUnitIndex.fromBuffer(indexBytes);
+  }
+
+  Future<TestResolvedUnitResult> _indexTestCode(String code) async {
+    var result = await resolveTestCodeWithDiagnostics(code);
+    _indexResult(result);
     return result;
   }
 
diff --git a/pkg/analyzer/test/src/dart/resolution/extension_method_test.dart b/pkg/analyzer/test/src/dart/resolution/extension_method_test.dart
index 618610e123b..f6682b4a62c 100644
--- a/pkg/analyzer/test/src/dart/resolution/extension_method_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/extension_method_test.dart
@@ -1383,20 +1383,21 @@ extension E on int {
 }
 ''');
 
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 import 'x.dart';
 void f() {
   0.foo();
 }
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, []);
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singleMethodInvocation;
     assertResolvedNodeText(node, r'''
diff --git a/pkg/analyzer/test/src/dart/resolution/library_export_test.dart b/pkg/analyzer/test/src/dart/resolution/library_export_test.dart
index 2279d052374..68440f0462f 100644
--- a/pkg/analyzer/test/src/dart/resolution/library_export_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/library_export_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -533,19 +532,20 @@ ExportDirective
   }
 
   test_inPart_library() async {
-    newFile('$testPackageLibPath/a.dart', r'''
-part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
-part of 'a.dart';
-export 'c.dart';
-''');
-
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
     newFile('$testPackageLibPath/c.dart', '');
 
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, const []);
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
+part 'b.dart';
+''',
+      b: r'''
+part of 'a.dart';
+export 'c.dart';
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.export('c.dart');
     assertResolvedNodeText(node, r'''
@@ -561,17 +561,20 @@ ExportDirective
   }
 
   test_inPart_library_fileDoesNotExist() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 export 'c.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.uriDoesNotExist, 25, 8)]);
+//     ^^^^^^^^
+// [diag.uriDoesNotExist] Target of URI doesn't exist: 'c.dart'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.export('c.dart');
     assertResolvedNodeText(node, r'''
@@ -587,17 +590,20 @@ ExportDirective
   }
 
   test_inPart_noRelativeUri() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 export ':net';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.invalidUri, 25, 6)]);
+//     ^^^^^^
+// [diag.invalidUri] Invalid URI syntax: ':net'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.export('export');
     assertResolvedNodeText(node, r'''
@@ -613,19 +619,20 @@ ExportDirective
   }
 
   test_inPart_noRelativeUriStr() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 export '${'foo'}.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [
-      error(diag.uriWithInterpolation, 25, 15),
-    ]);
+//     ^^^^^^^^^^^^^^^
+// [diag.uriWithInterpolation] URIs can't use string interpolation.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.export('export');
     assertResolvedNodeText(node, r'''
@@ -651,17 +658,20 @@ ExportDirective
   }
 
   test_inPart_noSource() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 export 'foo:bar';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.uriDoesNotExist, 25, 9)]);
+//     ^^^^^^^^^
+// [diag.uriDoesNotExist] Target of URI doesn't exist: 'foo:bar'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.export('export');
     assertResolvedNodeText(node, r'''
@@ -677,21 +687,24 @@ ExportDirective
   }
 
   test_inPart_notLibrary_partOfName() async {
-    newFile('$testPackageLibPath/a.dart', r'''
-part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
-part of 'a.dart';
-export 'c.dart';
-''');
-
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
     newFile('$testPackageLibPath/c.dart', r'''
 part of my.lib;
 ''');
 
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.exportOfNonLibrary, 25, 8)]);
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
+part 'b.dart';
+''',
+      b: r'''
+part of 'a.dart';
+export 'c.dart';
+//     ^^^^^^^^
+// [diag.exportOfNonLibrary] The exported library 'c.dart' can't have a part-of directive.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.export('c.dart');
     assertResolvedNodeText(node, r'''
@@ -707,21 +720,24 @@ ExportDirective
   }
 
   test_inPart_notLibrary_partOfUri() async {
-    newFile('$testPackageLibPath/a.dart', r'''
-part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
-part of 'a.dart';
-export 'c.dart';
-''');
-
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
     newFile('$testPackageLibPath/c.dart', r'''
 part of 'b.dart';
 ''');
 
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.exportOfNonLibrary, 25, 8)]);
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
+part 'b.dart';
+''',
+      b: r'''
+part of 'a.dart';
+export 'c.dart';
+//     ^^^^^^^^
+// [diag.exportOfNonLibrary] The exported library 'c.dart' can't have a part-of directive.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.export('c.dart');
     assertResolvedNodeText(node, r'''
diff --git a/pkg/analyzer/test/src/dart/resolution/library_import_test.dart b/pkg/analyzer/test/src/dart/resolution/library_import_test.dart
index dd5a3481d2f..7500c845aeb 100644
--- a/pkg/analyzer/test/src/dart/resolution/library_import_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/library_import_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'context_collection_resolution.dart';
@@ -716,22 +715,23 @@ ImportDirective
   }
 
   test_inPart_library() async {
-    newFile('$testPackageLibPath/a.dart', r'''
-part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
-part of 'a.dart';
-import 'c.dart';
-''');
-
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
     newFile('$testPackageLibPath/c.dart', '');
 
-    var result = await resolveFile2(b);
-    // TODO(scheglov): update the hint.
-    // assertErrorsInTestResult(result, [
-    //   error(WarningCode.UNUSED_IMPORT, 33, 8),
-    // ]);
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
+part 'b.dart';
+''',
+      b: r'''
+part of 'a.dart';
+import 'c.dart';
+//     ^^^^^^^^
+// [diag.unusedImport] Unused import: 'c.dart'.
+''',
+    });
+
+    var result = results[b]!;
 
     var node = result.findNode.import('c.dart');
     assertResolvedNodeText(node, r'''
@@ -747,17 +747,20 @@ ImportDirective
   }
 
   test_inPart_library_fileDoesNotExist() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 import 'c.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.uriDoesNotExist, 25, 8)]);
+//     ^^^^^^^^
+// [diag.uriDoesNotExist] Target of URI doesn't exist: 'c.dart'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.import('c.dart');
     assertResolvedNodeText(node, r'''
@@ -773,17 +776,20 @@ ImportDirective
   }
 
   test_inPart_noRelativeUri() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 import ':net';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.invalidUri, 25, 6)]);
+//     ^^^^^^
+// [diag.invalidUri] Invalid URI syntax: ':net'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.import('import');
     assertResolvedNodeText(node, r'''
@@ -799,19 +805,20 @@ ImportDirective
   }
 
   test_inPart_noRelativeUriStr() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 import '${'foo'}.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [
-      error(diag.uriWithInterpolation, 25, 15),
-    ]);
+//     ^^^^^^^^^^^^^^^
+// [diag.uriWithInterpolation] URIs can't use string interpolation.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.import('import');
     assertResolvedNodeText(node, r'''
@@ -837,17 +844,20 @@ ImportDirective
   }
 
   test_inPart_noSource() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 import 'foo:bar';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.uriDoesNotExist, 25, 9)]);
+//     ^^^^^^^^^
+// [diag.uriDoesNotExist] Target of URI doesn't exist: 'foo:bar'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.import('import');
     assertResolvedNodeText(node, r'''
@@ -863,21 +873,25 @@ ImportDirective
   }
 
   test_inPart_notLibrary_partOfName() async {
-    newFile('$testPackageLibPath/a.dart', r'''
-part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
-part of 'a.dart';
-import 'c.dart';
-''');
-
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
     newFile('$testPackageLibPath/c.dart', r'''
 part of my.lib;
 ''');
 
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.importOfNonLibrary, 25, 8)]);
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
+part 'b.dart';
+''',
+      b: r'''
+part of 'a.dart';
+import 'c.dart';
+//     ^^^^^^^^
+// [diag.importOfNonLibrary] The imported library 'c.dart' can't have a part-of directive.
+''',
+    });
+
+    var result = results[b]!;
 
     var node = result.findNode.import('c.dart');
     assertResolvedNodeText(node, r'''
@@ -893,21 +907,25 @@ ImportDirective
   }
 
   test_inPart_notLibrary_partOfUri() async {
-    newFile('$testPackageLibPath/a.dart', r'''
-part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
-part of 'a.dart';
-import 'c.dart';
-''');
-
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
     newFile('$testPackageLibPath/c.dart', r'''
 part of 'b.dart';
 ''');
 
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.importOfNonLibrary, 25, 8)]);
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
+part 'b.dart';
+''',
+      b: r'''
+part of 'a.dart';
+import 'c.dart';
+//     ^^^^^^^^
+// [diag.importOfNonLibrary] The imported library 'c.dart' can't have a part-of directive.
+''',
+    });
+
+    var result = results[b]!;
 
     var node = result.findNode.import('c.dart');
     assertResolvedNodeText(node, r'''
diff --git a/pkg/analyzer/test/src/dart/resolution/metadata_test.dart b/pkg/analyzer/test/src/dart/resolution/metadata_test.dart
index 0703fb2e439..a160682271b 100644
--- a/pkg/analyzer/test/src/dart/resolution/metadata_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/metadata_test.dart
@@ -344,18 +344,18 @@ const foo = 42;
   }
 
   test_location_partOfDirective() async {
-    newFile('$testPackageLibPath/test.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var results = await resolveFilesWithDiagnostics({
+      testFile: r'''
 part 'a.dart';
 const foo = 42;
-''');
-
-    var a = newFile('$testPackageLibPath/a.dart', r'''
+''',
+      a: r'''
 @foo
 part of 'test.dart';
-''');
-
-    var result = await resolveFile2(a);
-    assertErrorsInTestResult(result, const []);
+''',
+    });
+    var result = results[a]!;
 
     _assertAtFoo42(result);
   }
diff --git a/pkg/analyzer/test/src/dart/resolution/node_text_expectations.dart b/pkg/analyzer/test/src/dart/resolution/node_text_expectations.dart
index 51da3fc4dab..757e8ea2997 100644
--- a/pkg/analyzer/test/src/dart/resolution/node_text_expectations.dart
+++ b/pkg/analyzer/test/src/dart/resolution/node_text_expectations.dart
@@ -206,6 +206,11 @@ class NodeTextExpectationsCollector {
       methodName: 'resolveFilesWithDiagnostics',
       argument: _ArgumentMapEntryValue(mapArgument: _ArgumentIndex(0)),
     ),
+    _AssertMethod(
+      className: '_IndexMixin',
+      methodName: '_indexTestCode',
+      argument: _ArgumentIndex(0),
+    ),
     _AssertMethod(
       className: 'ResolutionTest',
       methodName: 'resolveTestCodeWithDiagnostics',
diff --git a/pkg/analyzer/test/src/dart/resolution/part_test.dart b/pkg/analyzer/test/src/dart/resolution/part_test.dart
index 96cd065d36d..f07be1c17c8 100644
--- a/pkg/analyzer/test/src/dart/resolution/part_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/part_test.dart
@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analyzer/src/dart/element/element.dart';
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -133,22 +132,20 @@ PartDirective
   }
 
   test_inLibrary_withPart_partOfName() async {
-    var a = newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 // @dart = 3.4
 library my.lib;
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 // @dart = 3.4
 part of my.lib;
-''');
-
-    var bResult = await resolveFile2(b);
-    assertErrorsInTestResult(bResult, const []);
-
-    var result = await resolveFile2(a);
-    assertErrorsInTestResult(result, const []);
+''',
+    });
+    var result = results[a]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -164,22 +161,20 @@ PartDirective
   }
 
   test_inLibrary_withPart_partOfName_preEnhancedParts() async {
-    var a = newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 // @dart = 3.4
 library my.lib;
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 // @dart = 3.4
 part of my.lib;
-''');
-
-    var bResult = await resolveFile2(b);
-    assertErrorsInTestResult(bResult, const []);
-
-    var result = await resolveFile2(a);
-    assertErrorsInTestResult(result, const []);
+''',
+    });
+    var result = results[a]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -195,24 +190,22 @@ PartDirective
   }
 
   test_inLibrary_withPart_partOfName_preEnhancedParts_different() async {
-    var a = newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 // @dart = 3.4
 library foo;
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+//   ^^^^^^^^
+// [diag.partOfDifferentLibrary] Expected this library to be part of 'foo', not 'bar'.
+''',
+      b: r'''
 // @dart = 3.4
 part of bar;
-''');
-
-    var bResult = await resolveFile2(b);
-    assertErrorsInTestResult(bResult, const []);
-
-    var result = await resolveFile2(a);
-    assertErrorsInTestResult(result, [
-      error(diag.partOfDifferentLibrary, 33, 8),
-    ]);
+''',
+    });
+    var result = results[a]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -324,17 +317,20 @@ PartDirective
   }
 
   test_inPart_fileDoesNotExist() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part 'c.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.uriDoesNotExist, 23, 8)]);
+//   ^^^^^^^^
+// [diag.uriDoesNotExist] Target of URI doesn't exist: 'package:test/c.dart'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -350,17 +346,20 @@ PartDirective
   }
 
   test_inPart_noRelativeUri() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part ':net';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.invalidUri, 23, 6)]);
+//   ^^^^^^
+// [diag.invalidUri] Invalid URI syntax: ':net'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -376,19 +375,20 @@ PartDirective
   }
 
   test_inPart_noRelativeUriStr() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part '${'foo'}.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [
-      error(diag.uriWithInterpolation, 23, 15),
-    ]);
+//   ^^^^^^^^^^^^^^^
+// [diag.uriWithInterpolation] URIs can't use string interpolation.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -414,17 +414,20 @@ PartDirective
   }
 
   test_inPart_noSource() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part 'foo:bar';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.uriDoesNotExist, 23, 9)]);
+//   ^^^^^^^^^
+// [diag.uriDoesNotExist] Target of URI doesn't exist: 'foo:bar'.
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -440,25 +443,26 @@ PartDirective
   }
 
   test_inPart_withPart_partOfName() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var c = getFile('$testPackageLibPath/c.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part 'c.dart';
-''');
-
-    var c = newFile('$testPackageLibPath/c.dart', r'''
+''',
+      c: r'''
 part of my.lib;
-''');
-
-    var cResult = await resolveFile2(c);
-    assertErrorsInTestResult(cResult, [error(diag.partOfName, 8, 6)]);
+//      ^^^^^^
+// [diag.partOfName] The 'part of' directive can't use a name with the enhanced-parts feature.
+''',
+    });
 
     // We already reported an error above.
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, const []);
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -474,21 +478,22 @@ PartDirective
   }
 
   test_inPart_withPart_partOfUri() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var c = getFile('$testPackageLibPath/c.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part 'c.dart';
-''');
-
-    newFile('$testPackageLibPath/c.dart', r'''
+''',
+      c: r'''
 part of 'b.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, const []);
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -504,23 +509,24 @@ PartDirective
   }
 
   test_inPart_withPart_partOfUri_different() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var c = getFile('$testPackageLibPath/c.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part 'c.dart';
-''');
-
-    newFile('$testPackageLibPath/c.dart', r'''
+//   ^^^^^^^^
+// [diag.partOfDifferentLibrary] Expected this library to be part of 'package:test/b.dart', not 'package:test/c.dart'.
+''',
+      c: r'''
 part of 'a.dart';
-''');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [
-      error(diag.partOfDifferentLibrary, 23, 8),
-    ]);
+''',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
@@ -536,19 +542,22 @@ PartDirective
   }
 
   test_inPart_withSource_notPart_library() async {
-    newFile('$testPackageLibPath/a.dart', r'''
+    var a = getFile('$testPackageLibPath/a.dart');
+    var b = getFile('$testPackageLibPath/b.dart');
+    var c = getFile('$testPackageLibPath/c.dart');
+    var results = await resolveFilesWithDiagnostics({
+      a: r'''
 part 'b.dart';
-''');
-
-    var b = newFile('$testPackageLibPath/b.dart', r'''
+''',
+      b: r'''
 part of 'a.dart';
 part 'c.dart';
-''');
-
-    newFile('$testPackageLibPath/c.dart', '');
-
-    var result = await resolveFile2(b);
-    assertErrorsInTestResult(result, [error(diag.partOfNonPart, 23, 8)]);
+//   ^^^^^^^^
+// [diag.partOfNonPart] The included part 'package:test/c.dart' must have a part-of directive.
+''',
+      c: '',
+    });
+    var result = results[b]!;
 
     var node = result.findNode.singlePartDirective;
     assertResolvedNodeText(node, r'''
diff --git a/pkg/analyzer/test/src/dart/resolution/resolution.dart b/pkg/analyzer/test/src/dart/resolution/resolution.dart
index 33cface2422..8458d8c736e 100644
--- a/pkg/analyzer/test/src/dart/resolution/resolution.dart
+++ b/pkg/analyzer/test/src/dart/resolution/resolution.dart
@@ -140,13 +140,6 @@ mixin ResolutionTest implements ResourceProviderMixin {
     diagnosticListener.assertErrors(expectedDiagnostics);
   }
 
-  void assertErrorsInTestResult(
-    TestResolvedUnitResult result,
-    List<ExpectedDiagnostic> expectedDiagnostics,
-  ) {
-    assertErrorsInList(result.diagnostics, expectedDiagnostics);
-  }
-
   void assertHasTestErrors(TestResolvedUnitResult result) {
     expect(result.diagnostics, isNotEmpty);
   }
diff --git a/pkg/analyzer/test/src/diagnostics/import_internal_library_test.dart b/pkg/analyzer/test/src/diagnostics/import_internal_library_test.dart
index 20b57795ca2..864e22e4f4f 100644
--- a/pkg/analyzer/test/src/diagnostics/import_internal_library_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/import_internal_library_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
 import 'package:analyzer_testing/package_config_file_builder.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -32,11 +31,12 @@ import 'dart:_internal';
 
   test_wasm_fromJs() async {
     var packageRootPath = _newPackage('js');
-    var file = newFile('$packageRootPath/lib/js.dart', '''
+    var file = getFile('$packageRootPath/lib/js.dart');
+    await resolveFileWithDiagnostics(file, '''
 import 'dart:_wasm';
+//     ^^^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'dart:_wasm'.
 ''');
-    var result = await resolveFile2(file);
-    assertErrorsInTestResult(result, [error(diag.unusedImport, 7, 12)]);
   }
 
   test_wasm_fromTest() async {
@@ -50,11 +50,12 @@ import 'dart:_wasm';
 
   test_wasm_fromUi() async {
     var packageRootPath = _newPackage('ui');
-    var file = newFile('$packageRootPath/lib/ui.dart', '''
+    var file = getFile('$packageRootPath/lib/ui.dart');
+    await resolveFileWithDiagnostics(file, '''
 import 'dart:_wasm';
+//     ^^^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'dart:_wasm'.
 ''');
-    var result = await resolveFile2(file);
-    assertErrorsInTestResult(result, [error(diag.unusedImport, 7, 12)]);
   }
 
   String _newPackage(String packageName) {
diff --git a/pkg/analyzer/test/src/diagnostics/invalid_export_of_internal_element_test.dart b/pkg/analyzer/test/src/diagnostics/invalid_export_of_internal_element_test.dart
index 6b3c5111fe6..2fedde7b4d4 100644
--- a/pkg/analyzer/test/src/diagnostics/invalid_export_of_internal_element_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/invalid_export_of_internal_element_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
 import 'package:analyzer_testing/mock_packages/mock_packages.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -47,16 +46,11 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    var result = await resolveFileCode(
-      '$testPackageBlazeBinPath/lib/bar.dart',
-      r'''
+    var file = getFile('$testPackageBlazeBinPath/lib/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'src/foo.dart';
-''',
-    );
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidExportOfInternalElement, 0, 22),
-    ]);
+// [diag.invalidExportOfInternalElement][column 1][length 22] The member 'One' can't be exported as a part of a package's public API.
+''');
   }
 
   void test_exporterIsInBlazeBinLibSrc() async {
@@ -65,12 +59,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageBlazeBinPath/lib/src/bar.dart'),
-      r'''
+    var file = getFile('$testPackageBlazeBinPath/lib/src/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'foo.dart';
-''',
-    );
+''');
   }
 
   void test_exporterIsInGenfilesLib() async {
@@ -79,16 +71,11 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    var result = await resolveFileCode(
-      '$testPackageGenfilesPath/lib/bar.dart',
-      r'''
+    var file = getFile('$testPackageGenfilesPath/lib/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'src/foo.dart';
-''',
-    );
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidExportOfInternalElement, 0, 22),
-    ]);
+// [diag.invalidExportOfInternalElement][column 1][length 22] The member 'One' can't be exported as a part of a package's public API.
+''');
   }
 
   void test_exporterIsInGenfilesLibSrc() async {
@@ -97,12 +84,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageGenfilesPath/lib/src/bar.dart'),
-      r'''
+    var file = getFile('$testPackageGenfilesPath/lib/src/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'foo.dart';
-''',
-    );
+''');
   }
 
   void test_exporterIsInLib() async {
@@ -111,13 +96,11 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    var result = await resolveFileCode('$testPackageLibPath/bar.dart', r'''
+    var file = getFile('$testPackageLibPath/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'src/foo.dart';
+// [diag.invalidExportOfInternalElement][column 1][length 22] The member 'One' can't be exported as a part of a package's public API.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidExportOfInternalElement, 0, 22),
-    ]);
   }
 
   void test_exporterIsInLibSrc() async {
@@ -126,12 +109,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageLibPath/src/bar.dart'),
-      r'''
+    var file = getFile('$testPackageLibPath/src/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'foo.dart';
-''',
-    );
+''');
   }
 
   void test_exporterIsInTest() async {
@@ -140,12 +121,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$myPackageRootPath/test/foo_test.dart'),
-      r'''
+    var file = getFile('$myPackageRootPath/test/foo_test.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'package:dart.my/src/foo.dart';
-''',
-    );
+''');
   }
 
   void test_internalIsInBlazeBin() async {
@@ -203,16 +182,11 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    var result = await resolveFileCode(
-      '$testPackageDartToolPath/lib/bar.dart',
-      r'''
+    var file = getFile('$testPackageDartToolPath/lib/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'package:test/src/foo.dart';
-''',
-    );
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidExportOfInternalElement, 0, 35),
-    ]);
+// [diag.invalidExportOfInternalElement][column 1][length 35] The member 'One' can't be exported as a part of a package's public API.
+''');
   }
 
   @FailingTest(
@@ -227,12 +201,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageDartToolPath/lib/src/bar.dart'),
-      r'''
+    var file = getFile('$testPackageDartToolPath/lib/src/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'package:test/src/foo.dart';
-''',
-    );
+''');
   }
 
   void test_exporterInLib() async {
@@ -241,13 +213,11 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    var result = await resolveFileCode('$testPackageRootPath/lib/bar.dart', r'''
+    var file = getFile('$testPackageRootPath/lib/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'package:test/src/foo.dart';
+// [diag.invalidExportOfInternalElement][column 1][length 35] The member 'One' can't be exported as a part of a package's public API.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidExportOfInternalElement, 0, 35),
-    ]);
   }
 
   void test_exporterInLibSrc() async {
@@ -256,12 +226,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageRootPath/lib/src/bar.dart'),
-      r'''
+    var file = getFile('$testPackageRootPath/lib/src/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'package:test/src/foo.dart';
-''',
-    );
+''');
   }
 
   void test_internalIsInGeneratedLibSrc() async {
@@ -310,13 +278,11 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    var result = await resolveFileCode('$testPackageLibPath/bar.dart', r'''
+    var file = getFile('$testPackageLibPath/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'src/foo.dart';
+// [diag.invalidExportOfInternalElement][column 1][length 22] The member 'One' can't be exported as a part of a package's public API.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidExportOfInternalElement, 0, 22),
-    ]);
   }
 
   void test_exporterIsInLibSrc() async {
@@ -325,12 +291,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageLibPath/src/bar.dart'),
-      r'''
+    var file = getFile('$testPackageLibPath/src/bar.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'foo.dart';
-''',
-    );
+''');
   }
 
   void test_exporterIsInTest() async {
@@ -339,12 +303,10 @@ import 'package:meta/meta.dart';
 @internal class One {}
 ''');
 
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageRootPath/test/foo_test.dart'),
-      r'''
+    var file = getFile('$testPackageRootPath/test/foo_test.dart');
+    await resolveFileWithDiagnostics(file, r'''
 export 'package:test/src/foo.dart';
-''',
-    );
+''');
   }
 
   void test_internalIsLibSrc() async {
diff --git a/pkg/analyzer/test/src/diagnostics/invalid_internal_annotation_test.dart b/pkg/analyzer/test/src/diagnostics/invalid_internal_annotation_test.dart
index fa3220b75f6..058a653e76f 100644
--- a/pkg/analyzer/test/src/diagnostics/invalid_internal_annotation_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/invalid_internal_annotation_test.dart
@@ -2,20 +2,22 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
+import 'package:analyzer/file_system/file_system.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../dart/resolution/context_collection_resolution.dart';
+import '../dart/resolution/node_text_expectations.dart';
 
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(InvalidInternalAnnotationTest);
+    defineReflectiveTests(UpdateNodeTextExpectations);
   });
 }
 
 @reflectiveTest
 class InvalidInternalAnnotationTest extends PubPackageResolutionTest {
-  String get testPackageLibSrcFilePath => '$testPackageLibPath/src/foo.dart';
+  File get testPackageLibSrcFile => getFile('$testPackageLibPath/src/foo.dart');
 
   @override
   void setUp() {
@@ -28,354 +30,312 @@ version: 0.0.1
   }
 
   void test_annotationInLib() async {
-    var result = await resolveFileCode('$testPackageLibPath/foo.dart', r'''
+    var file = getFile('$testPackageLibPath/foo.dart');
+    await resolveFileWithDiagnostics(file, r'''
 import 'package:meta/meta.dart';
 @internal class One {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-    ]);
   }
 
   void test_annotationInLib_onLibrary() async {
-    var result = await resolveFileCode('$testPackageLibPath/foo.dart', r'''
+    var file = getFile('$testPackageLibPath/foo.dart');
+    await resolveFileWithDiagnostics(file, r'''
 @internal
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
 library foo;
 import 'package:meta/meta.dart';
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 1, 8),
-    ]);
   }
 
   void test_annotationInLibSrc() async {
-    await resolveFileWithDiagnostics(getFile(testPackageLibSrcFilePath), r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal class One {}
 ''');
   }
 
   void test_annotationInLibSrcSubdirectory() async {
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageLibPath/src/foo/foo.dart'),
-      r'''
+    var file = getFile('$testPackageLibPath/src/foo/foo.dart');
+    await resolveFileWithDiagnostics(file, r'''
 import 'package:meta/meta.dart';
 @internal class One {}
-''',
-    );
+''');
   }
 
   void test_annotationInLibSubdirectory() async {
-    var result = await resolveFileCode('$testPackageLibPath/foo/foo.dart', r'''
+    var file = getFile('$testPackageLibPath/foo/foo.dart');
+    await resolveFileWithDiagnostics(file, r'''
 import 'package:meta/meta.dart';
 @internal class One {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-    ]);
   }
 
   void test_annotationInTest() async {
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageRootPath/test/foo_test.dart'),
-      r'''
+    var file = getFile('$testPackageRootPath/test/foo_test.dart');
+    await resolveFileWithDiagnostics(file, r'''
 import 'package:meta/meta.dart';
 @internal class One {}
-''',
-    );
+''');
   }
 
   void test_annotationInTest_extensionType() async {
-    await resolveFileWithDiagnostics(
-      getFile('$testPackageRootPath/test/foo_test.dart'),
-      r'''
+    var file = getFile('$testPackageRootPath/test/foo_test.dart');
+    await resolveFileWithDiagnostics(file, r'''
 import 'package:meta/meta.dart';
 @internal extension type E(int i) {}
-''',
-    );
+''');
   }
 
   void test_privateClass() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal class _One {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
+//              ^^^^
+// [diag.unusedElement] The declaration '_One' isn't referenced.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-      error(diag.unusedElement, 49, 4),
-    ]);
   }
 
   void test_privateConstructor() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class C {
   @internal C._f();
+// ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 46, 8),
-    ]);
   }
 
   void test_privateEnum() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal enum _E {one}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
+//             ^^
+// [diag.unusedElement] The declaration '_E' isn't referenced.
+//                 ^^^
+// [diag.unusedField] The value of the field 'one' isn't used.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-      error(diag.unusedElement, 48, 2),
-      error(diag.unusedField, 52, 3),
-    ]);
   }
 
   void test_privateEnumValue() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 enum E {@internal _one}
+//       ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
+//                ^^^^
+// [diag.unusedField] The value of the field '_one' isn't used.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 42, 8),
-      error(diag.unusedField, 51, 4),
-    ]);
   }
 
   void test_privateExtension() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal extension _One on String {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-    ]);
   }
 
   void test_privateExtension_unnamed() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal extension on String {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-    ]);
   }
 
   void test_privateExtensionType() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal extension type _E(int i) {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
+//                       ^^
+// [diag.unusedElement] The declaration '_E' isn't referenced.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-      error(diag.unusedElement, 58, 2),
-    ]);
   }
 
   void test_privateField_instance() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class C {
   @internal int _i = 0;
+//              ^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
+//              ^^
+// [diag.unusedField] The value of the field '_i' isn't used.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.unusedField, 59, 2),
-      error(diag.invalidInternalAnnotation, 59, 6),
-    ]);
   }
 
   void test_privateField_static() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class C {
   @internal static int _i = 0;
+//                     ^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
+//                     ^^
+// [diag.unusedField] The value of the field '_i' isn't used.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.unusedField, 66, 2),
-      error(diag.invalidInternalAnnotation, 66, 6),
-    ]);
   }
 
   void test_privateGetter() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class C {
   @internal int get _i => 0;
+// ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
+//                  ^^
+// [diag.unusedElement] The declaration '_i' isn't referenced.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 46, 8),
-      error(diag.unusedElement, 63, 2),
-    ]);
   }
 
   void test_privateMethod_instance() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class C {
   @internal void _f() {}
+// ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
+//               ^^
+// [diag.unusedElement] The declaration '_f' isn't referenced.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 46, 8),
-      error(diag.unusedElement, 60, 2),
-    ]);
   }
 
   void test_privateMethod_static() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class C {
   @internal static void _f() {}
+// ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
+//                      ^^
+// [diag.unusedElement] The declaration '_f' isn't referenced.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 46, 8),
-      error(diag.unusedElement, 67, 2),
-    ]);
   }
 
   void test_privateMixin() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal mixin _One {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
+//              ^^^^
+// [diag.unusedElement] The declaration '_One' isn't referenced.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-      error(diag.unusedElement, 49, 4),
-    ]);
   }
 
   void test_privateTopLevelFunction() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal void _f() {}
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
+//             ^^
+// [diag.unusedElement] The declaration '_f' isn't referenced.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-      error(diag.unusedElement, 48, 2),
-    ]);
   }
 
   void test_privateTopLevelVariable() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal int _i = 1;
+//            ^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
+//            ^^
+// [diag.unusedElement] The declaration '_i' isn't referenced.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 47, 6),
-      error(diag.unusedElement, 47, 2),
-    ]);
   }
 
   void test_privateTypedef() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 @internal typedef _T = void Function();
+// [diag.invalidInternalAnnotation][column 2][length 8] Only public elements in a package's private API can be annotated as being internal.
+//                ^^
+// [diag.unusedElement] The declaration '_T' isn't referenced.
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.invalidInternalAnnotation, 34, 8),
-      error(diag.unusedElement, 51, 2),
-    ]);
   }
 
   void test_publicConstructor_named_privateClass() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class _C {
+//    ^^
+// [diag.unusedElement] The declaration '_C' isn't referenced.
   @internal _C.named();
+// ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.unusedElement, 39, 2),
-      error(diag.invalidInternalAnnotation, 47, 8),
-    ]);
   }
 
   void test_publicConstructor_primary_privateClass() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class _C() {
+//    ^^
+// [diag.unusedElement] The declaration '_C' isn't referenced.
   @internal
+// ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
   this;
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.unusedElement, 39, 2),
-      error(diag.invalidInternalAnnotation, 49, 8),
-    ]);
   }
 
   void test_publicConstructor_unnamed_privateClass() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class _C {
+//    ^^
+// [diag.unusedElement] The declaration '_C' isn't referenced.
   @internal _C();
+// ^^^^^^^^
+// [diag.invalidInternalAnnotation] Only public elements in a package's private API can be annotated as being internal.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.unusedElement, 39, 2),
-      error(diag.invalidInternalAnnotation, 47, 8),
-    ]);
   }
 
   void test_publicMethod_privateClass() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class _C {
+//    ^^
+// [diag.unusedElement] The declaration '_C' isn't referenced.
   @internal void f() {}
 }
 ''');
-
-    assertErrorsInTestResult(result, [error(diag.unusedElement, 39, 2)]);
   }
 
   void test_publicMethod_privateClass_static() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 class _C {
+//    ^^
+// [diag.unusedElement] The declaration '_C' isn't referenced.
   @internal static void f() {}
+//                      ^
+// [diag.unusedElement] The declaration 'f' isn't referenced.
 }
 ''');
-
-    assertErrorsInTestResult(result, [
-      error(diag.unusedElement, 39, 2),
-      error(diag.unusedElement, 68, 1),
-    ]);
   }
 
   void test_publicMethod_privateExtensionType() async {
-    var result = await resolveFileCode(testPackageLibSrcFilePath, r'''
+    await resolveFileWithDiagnostics(testPackageLibSrcFile, r'''
 import 'package:meta/meta.dart';
 extension type _E(int i) {
+//             ^^
+// [diag.unusedElement] The declaration '_E' isn't referenced.
   @internal void f() {}
 }
 ''');
-
-    assertErrorsInTestResult(result, [error(diag.unusedElement, 48, 2)]);
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/uri_does_not_exist_test.dart b/pkg/analyzer/test/src/diagnostics/uri_does_not_exist_test.dart
index 3085dff9248..3e8a0398906 100644
--- a/pkg/analyzer/test/src/diagnostics/uri_does_not_exist_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/uri_does_not_exist_test.dart
@@ -2,7 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:analyzer/src/diagnostic/diagnostic.dart' as diag;
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import '../dart/resolution/context_collection_resolution.dart';
@@ -85,8 +84,11 @@ import 'target.dart';
     analysisDriver.removeFile(filePath);
     await analysisDriver.applyPendingFileChanges();
 
-    var result = await resolveTestFile();
-    assertErrorsInTestResult(result, [error(diag.uriDoesNotExist, 7, 13)]);
+    await resolveFileWithDiagnostics(testFile, '''
+import 'target.dart';
+//     ^^^^^^^^^^^^^
+// [diag.uriDoesNotExist] Target of URI doesn't exist: 'target.dart'.
+''');
   }
 
   test_libraryImport_cannotResolve() async {
@@ -116,7 +118,6 @@ main() {
 ''');
   }
 
-  @failingTest
   test_libraryImport_disappears_when_fixed() async {
     await resolveTestCodeWithDiagnostics('''
 import 'target.dart';
@@ -124,13 +125,17 @@ import 'target.dart';
 // [diag.uriDoesNotExist] Target of URI doesn't exist: 'target.dart'.
 ''');
 
-    newFile('$testPackageLibPath/target.dart', '');
+    var targetFile = newFile('$testPackageLibPath/target.dart', '');
 
-    // Make sure the error goes away.
-    // TODO(brianwilkerson): The error does not go away, possibly because the
-    //  file is not being reanalyzed.
-    var result = await resolveTestFile();
-    assertErrorsInTestResult(result, [error(diag.unusedImport, 0, 0)]);
+    var analysisDriver = driverFor(testFile);
+    analysisDriver.changeFile2(targetFile);
+    await analysisDriver.applyPendingFileChanges();
+
+    await resolveFileWithDiagnostics(testFile, '''
+import 'target.dart';
+//     ^^^^^^^^^^^^^
+// [diag.unusedImport] Unused import: 'target.dart'.
+''');
   }
 
   test_part() async {