diff --git a/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart b/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
index 13f7dab51c2..d963d9afebb 100644
--- a/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
+++ b/pkg/analyzer/test/src/dart/resolution/context_collection_resolution.dart
@@ -25,7 +25,7 @@ import 'package:analyzer_testing/experiments/experiments.dart';
 import 'package:analyzer_testing/mock_packages/mock_packages.dart';
 import 'package:analyzer_testing/package_config_file_builder.dart';
 import 'package:analyzer_testing/resource_provider_mixin.dart';
-import 'package:analyzer_testing/src/analysis_rule/pub_package_resolution.dart';
+import 'package:analyzer_testing/src/expected_diagnostics.dart';
 import 'package:analyzer_testing/utilities/utilities.dart';
 import 'package:analyzer_utilities/testing/tree_string_sink.dart';
 import 'package:linter/src/rules.dart';
@@ -460,14 +460,11 @@ mixin WithoutPrivateNamedParametersMixin on PubPackageResolutionTest {
 
 mixin WithStrictCastsMixin on PubPackageResolutionTest {
   /// Asserts that no errors are reported in [code] when implicit casts are
-  /// allowed, and that [expectedErrors] are reported for the same [code] when
-  /// implicit casts are not allowed.
-  Future<void> assertErrorsWithStrictCasts(
-    String code,
-    List<ExpectedError> expectedErrors,
-  ) async {
-    var result = await resolveTestCode(code);
-    assertErrorsInTestResult(result, const []);
+  /// allowed, and that the inline diagnostic expectations are reported for the
+  /// same [code] when implicit casts are not allowed.
+  Future<void> assertTestCodeWithStrictCastsDiagnostics(String code) async {
+    var cleanCode = removeDiagnosticExpectations(code);
+    await resolveTestCodeWithDiagnostics(cleanCode);
 
     await disposeAnalysisContextCollection();
 
@@ -475,12 +472,6 @@ mixin WithStrictCastsMixin on PubPackageResolutionTest {
       analysisOptionsContent(experiments: experiments, strictCasts: true),
     );
 
-    result = await resolveTestFile();
-    assertErrorsInTestResult(result, expectedErrors);
+    await resolveTestCodeWithDiagnostics(code);
   }
-
-  /// Asserts that no errors are reported in [code], both when implicit casts
-  /// are allowed and when implicit casts are not allowed.
-  Future<void> assertNoErrorsWithStrictCasts(String code) async =>
-      assertErrorsWithStrictCasts(code, []);
 }
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 27868601473..51da3fc4dab 100644
--- a/pkg/analyzer/test/src/dart/resolution/node_text_expectations.dart
+++ b/pkg/analyzer/test/src/dart/resolution/node_text_expectations.dart
@@ -196,6 +196,11 @@ class NodeTextExpectationsCollector {
       methodName: 'resolveFileWithDiagnostics',
       argument: _ArgumentIndex(1),
     ),
+    _AssertMethod(
+      className: 'WithStrictCastsMixin',
+      methodName: 'assertTestCodeWithStrictCastsDiagnostics',
+      argument: _ArgumentIndex(0),
+    ),
     _AssertMethod(
       className: 'ResolutionTest',
       methodName: 'resolveFilesWithDiagnostics',
diff --git a/pkg/analyzer/test/src/diagnostics/argument_type_not_assignable_test.dart b/pkg/analyzer/test/src/diagnostics/argument_type_not_assignable_test.dart
index 2d793d1a871..4acfe248eea 100644
--- a/pkg/analyzer/test/src/diagnostics/argument_type_not_assignable_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/argument_type_not_assignable_test.dart
@@ -770,37 +770,34 @@ class ArgumentTypeNotAssignableWithStrictCastsTest
     extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_extensionTypePrimaryConstructor() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 extension type E(int i) {}
 
 dynamic a;
 var e = E(a);
-''',
-      [error(diag.argumentTypeNotAssignable, 49, 1)],
-    );
+//        ^
+// [diag.argumentTypeNotAssignable] The argument type 'dynamic' can't be assigned to the parameter type 'int'.
+''');
   }
 
   test_functionCall() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(int i) {}
 void foo(dynamic a) {
   f(a);
+//  ^
+// [diag.argumentTypeNotAssignable] The argument type 'dynamic' can't be assigned to the parameter type 'int'.
 }
-''',
-      [error(diag.argumentTypeNotAssignable, 43, 1)],
-    );
+''');
   }
 
   test_operator() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void foo(int i, dynamic a) {
   i + a;
+//    ^
+// [diag.argumentTypeNotAssignable] The argument type 'dynamic' can't be assigned to the parameter type 'num'.
 }
-''',
-      [error(diag.argumentTypeNotAssignable, 35, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/field_initializer_not_assignable_test.dart b/pkg/analyzer/test/src/diagnostics/field_initializer_not_assignable_test.dart
index 01d262e53de..2b5645a8216 100644
--- a/pkg/analyzer/test/src/diagnostics/field_initializer_not_assignable_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/field_initializer_not_assignable_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';
@@ -57,26 +56,24 @@ class FieldInitializerNotAssignableWithStrictCastsTest
     extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_constructorInitializer() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 class A {
   int i;
   A(dynamic a) : i = a;
+//                   ^
+// [diag.fieldInitializerNotAssignable] The initializer type 'dynamic' can't be assigned to the field type 'int'.
 }
-''',
-      [error(diag.fieldInitializerNotAssignable, 40, 1)],
-    );
+''');
   }
 
   test_constructorInitializer_primaryConstructor() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 class A(dynamic a) {
   int i;
   this : i = a;
+//           ^
+// [diag.fieldInitializerNotAssignable] The initializer type 'dynamic' can't be assigned to the field type 'int'.
 }
-''',
-      [error(diag.fieldInitializerNotAssignable, 43, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/for_in_of_invalid_type_test.dart b/pkg/analyzer/test/src/diagnostics/for_in_of_invalid_type_test.dart
index 47819af3fca..78030e3b8fb 100644
--- a/pkg/analyzer/test/src/diagnostics/for_in_of_invalid_type_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/for_in_of_invalid_type_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';
@@ -161,15 +160,14 @@ f(Object e) async {
 class ForInOfInvalidTypeWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_forIn() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 f(dynamic e) {
   for (var id in e) {
+//               ^
+// [diag.forInOfInvalidType] The type 'dynamic' used in the 'for' loop must implement 'Iterable'.
     id;
   }
 }
-''',
-      [error(diag.forInOfInvalidType, 32, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/invalid_assignment_test.dart b/pkg/analyzer/test/src/diagnostics/invalid_assignment_test.dart
index b22e7636f4d..5096bc3f7a0 100644
--- a/pkg/analyzer/test/src/diagnostics/invalid_assignment_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/invalid_assignment_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';
@@ -1075,32 +1074,29 @@ main() {
 class InvalidAssignmentWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_functionType() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 dynamic a;
 void Function(int i) f = a;
-''',
-      [error(diag.invalidAssignment, 36, 1)],
-    );
+//                       ^
+// [diag.invalidAssignment] A value of type 'dynamic' can't be assigned to a variable of type 'void Function(int)'.
+''');
   }
 
   test_interfaceType() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 dynamic a;
 int b = a;
-''',
-      [error(diag.invalidAssignment, 19, 1)],
-    );
+//      ^
+// [diag.invalidAssignment] A value of type 'dynamic' can't be assigned to a variable of type 'int'.
+''');
   }
 
   test_recordType() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 dynamic a;
 (int i, ) r = a;
-''',
-      [error(diag.invalidAssignment, 25, 1)],
-    );
+//            ^
+// [diag.invalidAssignment] A value of type 'dynamic' can't be assigned to a variable of type '(int,)'.
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/list_element_type_not_assignable_test.dart b/pkg/analyzer/test/src/diagnostics/list_element_type_not_assignable_test.dart
index c74e217c3c7..d7526859858 100644
--- a/pkg/analyzer/test/src/diagnostics/list_element_type_not_assignable_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/list_element_type_not_assignable_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';
@@ -233,35 +232,32 @@ class ListElementTypeNotAssignableWithStrictCastsTest
     extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_ifElement_falseBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int>[if (c) 0 else a];
+//                    ^
+// [diag.listElementTypeNotAssignable] The element type 'dynamic' can't be assigned to the list type 'int'.
 }
-''',
-      [error(diag.listElementTypeNotAssignable, 50, 1)],
-    );
+''');
   }
 
   test_ifElement_trueBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int>[if (c) a];
+//             ^
+// [diag.listElementTypeNotAssignable] The element type 'dynamic' can't be assigned to the list type 'int'.
 }
-''',
-      [error(diag.listElementTypeNotAssignable, 43, 1)],
-    );
+''');
   }
 
   test_spread() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(Iterable<dynamic> a) {
   <int>[...a];
+//         ^
+// [diag.listElementTypeNotAssignable] The element type 'dynamic' can't be assigned to the list type 'int'.
 }
-''',
-      [error(diag.listElementTypeNotAssignable, 41, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/map_key_type_not_assignable_test.dart b/pkg/analyzer/test/src/diagnostics/map_key_type_not_assignable_test.dart
index c6c70a4be4e..09e1a14189a 100644
--- a/pkg/analyzer/test/src/diagnostics/map_key_type_not_assignable_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/map_key_type_not_assignable_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';
@@ -238,35 +237,32 @@ class MapKeyTypeNotAssignableWithStrictCastsTest
     extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_ifElement_falseBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int, int>{if (c) 0: 0 else a: 0};
+//                            ^
+// [diag.mapKeyTypeNotAssignable] The element type 'dynamic' can't be assigned to the map key type 'int'.
 }
-''',
-      [error(diag.mapKeyTypeNotAssignable, 58, 1)],
-    );
+''');
   }
 
   test_ifElement_trueBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int, int>{if (c) a: 0 };
+//                  ^
+// [diag.mapKeyTypeNotAssignable] The element type 'dynamic' can't be assigned to the map key type 'int'.
 }
-''',
-      [error(diag.mapKeyTypeNotAssignable, 48, 1)],
-    );
+''');
   }
 
   test_spread() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(Map<dynamic, int> a) {
   <int, int>{...a};
+//              ^
+// [diag.mapKeyTypeNotAssignable] The element type 'dynamic' can't be assigned to the map key type 'int'.
 }
-''',
-      [error(diag.mapKeyTypeNotAssignable, 46, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/map_value_type_not_assignable_test.dart b/pkg/analyzer/test/src/diagnostics/map_value_type_not_assignable_test.dart
index e9e68a90916..927c096830f 100644
--- a/pkg/analyzer/test/src/diagnostics/map_value_type_not_assignable_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/map_value_type_not_assignable_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';
@@ -232,35 +231,32 @@ class MapValueTypeNotAssignableWithStrictCastsTest
     extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_ifElement_falseBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int, int>{if (c) 0: 0 else 0: a};
+//                               ^
+// [diag.mapValueTypeNotAssignable] The element type 'dynamic' can't be assigned to the map value type 'int'.
 }
-''',
-      [error(diag.mapValueTypeNotAssignable, 61, 1)],
-    );
+''');
   }
 
   test_ifElement_trueBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int, int>{if (c) 0: a};
+//                     ^
+// [diag.mapValueTypeNotAssignable] The element type 'dynamic' can't be assigned to the map value type 'int'.
 }
-''',
-      [error(diag.mapValueTypeNotAssignable, 51, 1)],
-    );
+''');
   }
 
   test_spread() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(Map<int, dynamic> a) {
   <int, int>{...a};
+//              ^
+// [diag.mapValueTypeNotAssignable] The element type 'dynamic' can't be assigned to the map value type 'int'.
 }
-''',
-      [error(diag.mapValueTypeNotAssignable, 46, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/non_bool_condition_test.dart b/pkg/analyzer/test/src/diagnostics/non_bool_condition_test.dart
index 76acd2b159a..bc11dbf60b9 100644
--- a/pkg/analyzer/test/src/diagnostics/non_bool_condition_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/non_bool_condition_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';
@@ -292,24 +291,22 @@ f(Object o) {
 class NonBoolConditionWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_map_ifElement_condition() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(dynamic c) {
   <int, int>{if (c) 0: 0};
+//               ^
+// [diag.nonBoolCondition] Conditions must have a static type of 'bool'.
 }
-''',
-      [error(diag.nonBoolCondition, 37, 1)],
-    );
+''');
   }
 
   test_set_ifElement_condition() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(dynamic c) {
   <int>{if (c) 0};
+//          ^
+// [diag.nonBoolCondition] Conditions must have a static type of 'bool'.
 }
-''',
-      [error(diag.nonBoolCondition, 32, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/non_bool_expression_test.dart b/pkg/analyzer/test/src/diagnostics/non_bool_expression_test.dart
index 2e9929c1337..5807558084a 100644
--- a/pkg/analyzer/test/src/diagnostics/non_bool_expression_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/non_bool_expression_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';
@@ -55,13 +54,12 @@ f() {
 class NonBoolExpressionWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_assert() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(dynamic a) {
   assert(a);
+//       ^
+// [diag.nonBoolExpression] The expression in an assert must be of type 'bool'.
 }
-''',
-      [error(diag.nonBoolExpression, 29, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/non_bool_negation_expression_test.dart b/pkg/analyzer/test/src/diagnostics/non_bool_negation_expression_test.dart
index 339f6604471..c67a283e904 100644
--- a/pkg/analyzer/test/src/diagnostics/non_bool_negation_expression_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/non_bool_negation_expression_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';
@@ -64,13 +63,12 @@ class NonBoolNegationExpressionWithStrictCastsTest
     extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_negation() async {
-    await assertErrorsWithStrictCasts(
-      r'''
+    await assertTestCodeWithStrictCastsDiagnostics(r'''
 void f(dynamic a) {
   !a;
+// ^
+// [diag.nonBoolNegationExpression] A negation operand must have a static type of 'bool'.
 }
-''',
-      [error(diag.nonBoolNegationExpression, 23, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/non_bool_operand_test.dart b/pkg/analyzer/test/src/diagnostics/non_bool_operand_test.dart
index 628d3cf855b..42ac6a705ad 100644
--- a/pkg/analyzer/test/src/diagnostics/non_bool_operand_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/non_bool_operand_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';
@@ -115,13 +114,12 @@ bool f(bool left, double right) {
 class NonBoolOperandWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_and() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(dynamic a) {
   if(a && true) {}
+//   ^
+// [diag.nonBoolOperand] The operands of the operator '&&' must be assignable to 'bool'.
 }
-''',
-      [error(diag.nonBoolOperand, 25, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/not_iterable_spread_test.dart b/pkg/analyzer/test/src/diagnostics/not_iterable_spread_test.dart
index 515ee72105d..03a8b66cea1 100644
--- a/pkg/analyzer/test/src/diagnostics/not_iterable_spread_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/not_iterable_spread_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';
@@ -121,24 +120,22 @@ List<int> f() => [...{1: 2, 3: 4}];
 class NotIterableSpreadWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_list() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(dynamic a) {
   [...a];
+//    ^
+// [diag.notIterableSpread] Spread elements in list or set literals must implement 'Iterable'.
 }
-''',
-      [error(diag.notIterableSpread, 26, 1)],
-    );
+''');
   }
 
   test_set() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(dynamic a) {
   <int>{...a};
+//         ^
+// [diag.notIterableSpread] Spread elements in list or set literals must implement 'Iterable'.
 }
-''',
-      [error(diag.notIterableSpread, 31, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/not_map_spread_test.dart b/pkg/analyzer/test/src/diagnostics/not_map_spread_test.dart
index d74c068430a..e3b3679b08a 100644
--- a/pkg/analyzer/test/src/diagnostics/not_map_spread_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/not_map_spread_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';
@@ -103,13 +102,12 @@ void f<T extends num>(T a) {
 class NotMapSpreadWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_map() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(dynamic a) {
   <int, String>{...a};
+//                 ^
+// [diag.notMapSpread] Spread elements in map literals must implement 'Map'.
 }
-''',
-      [error(diag.notMapSpread, 39, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_test.dart b/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_test.dart
index d185575f639..f9f0d75b9b9 100644
--- a/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_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';
@@ -556,22 +555,20 @@ Map<int, int> f() => {...[1, 2, 3, 4]};
 class ReturnOfInvalidTypeWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_return() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 int f(dynamic a) => a;
-''',
-      [error(diag.returnOfInvalidTypeFromFunction, 20, 1)],
-    );
+//                  ^
+// [diag.returnOfInvalidTypeFromFunction] A value of type 'dynamic' can't be returned from the function 'f' because it has a return type of 'int'.
+''');
   }
 
   test_return_async() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 Future<int> f(dynamic a) async {
   return a;
+//       ^
+// [diag.returnOfInvalidTypeFromFunction] A value of type 'dynamic' can't be returned from the function 'f' because it has a return type of 'Future<int>'.
 }
-''',
-      [error(diag.returnOfInvalidTypeFromFunction, 42, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/set_element_type_not_assignable_test.dart b/pkg/analyzer/test/src/diagnostics/set_element_type_not_assignable_test.dart
index 3d04d52a8d3..e203d5f33b5 100644
--- a/pkg/analyzer/test/src/diagnostics/set_element_type_not_assignable_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/set_element_type_not_assignable_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';
@@ -198,35 +197,32 @@ class SetElementTypeNotAssignableWithStrictCastsTest
     extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_ifElement_falseBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int>{if (c) 0 else a};
+//                    ^
+// [diag.setElementTypeNotAssignable] The element type 'dynamic' can't be assigned to the set type 'int'.
 }
-''',
-      [error(diag.setElementTypeNotAssignable, 50, 1)],
-    );
+''');
   }
 
   test_ifElement_trueBranch() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(bool c, dynamic a) {
   <int>{if (c) a};
+//             ^
+// [diag.setElementTypeNotAssignable] The element type 'dynamic' can't be assigned to the set type 'int'.
 }
-''',
-      [error(diag.setElementTypeNotAssignable, 43, 1)],
-    );
+''');
   }
 
   test_spread() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 void f(Iterable<dynamic> a) {
   <int>{...a};
+//         ^
+// [diag.setElementTypeNotAssignable] The element type 'dynamic' can't be assigned to the set type 'int'.
 }
-''',
-      [error(diag.setElementTypeNotAssignable, 41, 1)],
-    );
+''');
   }
 }
diff --git a/pkg/analyzer/test/src/diagnostics/yield_of_invalid_type_test.dart b/pkg/analyzer/test/src/diagnostics/yield_of_invalid_type_test.dart
index 7e0405130ce..a2569beeb37 100644
--- a/pkg/analyzer/test/src/diagnostics/yield_of_invalid_type_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/yield_of_invalid_type_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';
@@ -465,24 +464,22 @@ Iterable<String> g() => throw 0;
 class YieldOfInvalidTypeWithStrictCastsTest extends PubPackageResolutionTest
     with WithStrictCastsMixin {
   test_yieldEach_asyncStar() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 f(dynamic a) async* {
   yield* a;
+//       ^
+// [diag.yieldEachOfInvalidType] The type 'dynamic' implied by the 'yield*' expression must be assignable to 'Stream<dynamic>'.
 }
-''',
-      [error(diag.yieldEachOfInvalidType, 31, 1)],
-    );
+''');
   }
 
   test_yieldEach_syncStar() async {
-    await assertErrorsWithStrictCasts(
-      '''
+    await assertTestCodeWithStrictCastsDiagnostics('''
 f(dynamic a) sync* {
   yield* a;
+//       ^
+// [diag.yieldEachOfInvalidType] The type 'dynamic' implied by the 'yield*' expression must be assignable to 'Iterable<dynamic>'.
 }
-''',
-      [error(diag.yieldEachOfInvalidType, 30, 1)],
-    );
+''');
   }
 }