diff --git a/pkg/analyzer/test/src/dart/resolution/language_version_test.dart b/pkg/analyzer/test/src/dart/resolution/language_version_test.dart
index c94064bcfd1..bafbda4b930 100644
--- a/pkg/analyzer/test/src/dart/resolution/language_version_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/language_version_test.dart
@@ -18,8 +18,7 @@ main() {
 }
 
 @reflectiveTest
-class NullSafetyExperimentGlobalTest extends _FeaturesTest
-    with WithNullSafetyMixin {
+class NullSafetyExperimentGlobalTest extends _FeaturesTest {
   test_jsonConfig_legacyContext_nonNullDependency() async {
     _configureTestWithJsonConfig('''
 {
diff --git a/pkg/analyzer/test/src/dart/resolution/type_inference/local_variable_test.dart b/pkg/analyzer/test/src/dart/resolution/type_inference/local_variable_test.dart
index 5d3126f62f6..556c1d0b07c 100644
--- a/pkg/analyzer/test/src/dart/resolution/type_inference/local_variable_test.dart
+++ b/pkg/analyzer/test/src/dart/resolution/type_inference/local_variable_test.dart
@@ -9,13 +9,25 @@ import '../context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(LocalVariableTest);
-    defineReflectiveTests(LocalVariableWithNullSafetyTest);
+    defineReflectiveTests(LocalVariableWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class LocalVariableTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with LocalVariableTestCases {
+  test_Never() async {
+    await resolveTestCode('''
+void f(Never a) {
+  var v = a;
+  v;
+}
+''');
+    _assertTypeOfV('Never');
+  }
+}
+
+mixin LocalVariableTestCases on PubPackageResolutionTest {
   test_int() async {
     await resolveTestCode('''
 void f() {
@@ -43,15 +55,5 @@ void f() {
 }
 
 @reflectiveTest
-class LocalVariableWithNullSafetyTest extends LocalVariableTest
-    with WithNullSafetyMixin {
-  test_Never() async {
-    await resolveTestCode('''
-void f(Never a) {
-  var v = a;
-  v;
-}
-''');
-    _assertTypeOfV('Never');
-  }
-}
+class LocalVariableWithoutNullSafetyTest extends PubPackageResolutionTest
+    with LocalVariableTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/missing_enum_constant_in_switch_test.dart b/pkg/analyzer/test/src/diagnostics/missing_enum_constant_in_switch_test.dart
index e3523e4e933..7ea89723564 100644
--- a/pkg/analyzer/test/src/diagnostics/missing_enum_constant_in_switch_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/missing_enum_constant_in_switch_test.dart
@@ -10,13 +10,63 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(MissingEnumConstantInSwitchTest);
-    defineReflectiveTests(MissingEnumConstantInSwitchWithNullSafetyTest);
+    defineReflectiveTests(MissingEnumConstantInSwitchWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class MissingEnumConstantInSwitchTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with MissingEnumConstantInSwitchTestCases {
+  test_nullable() async {
+    await assertErrorsInCode('''
+enum E { one, two }
+
+void f(E? e) {
+  switch (e) {
+    case E.one:
+    case E.two:
+      break;
+  }
+}
+''', [
+      error(StaticWarningCode.MISSING_ENUM_CONSTANT_IN_SWITCH, 38, 10),
+    ]);
+  }
+
+  test_nullable_default() async {
+    await assertNoErrorsInCode('''
+enum E { one, two }
+
+void f(E? e) {
+  switch (e) {
+    case E.one:
+      break;
+    default:
+      break;
+  }
+}
+''');
+  }
+
+  test_nullable_null() async {
+    await assertNoErrorsInCode('''
+enum E { one, two }
+
+void f(E? e) {
+  switch (e) {
+    case E.one:
+      break;
+    case E.two:
+      break;
+    case null:
+      break;
+  }
+}
+''');
+  }
+}
+
+mixin MissingEnumConstantInSwitchTestCases on PubPackageResolutionTest {
   test_default() async {
     await assertNoErrorsInCode('''
 enum E { one, two, three }
@@ -99,53 +149,6 @@ void f(E e) {
 }
 
 @reflectiveTest
-class MissingEnumConstantInSwitchWithNullSafetyTest
-    extends MissingEnumConstantInSwitchTest with WithNullSafetyMixin {
-  test_nullable() async {
-    await assertErrorsInCode('''
-enum E { one, two }
-
-void f(E? e) {
-  switch (e) {
-    case E.one:
-    case E.two:
-      break;
-  }
-}
-''', [
-      error(StaticWarningCode.MISSING_ENUM_CONSTANT_IN_SWITCH, 38, 10),
-    ]);
-  }
-
-  test_nullable_default() async {
-    await assertNoErrorsInCode('''
-enum E { one, two }
-
-void f(E? e) {
-  switch (e) {
-    case E.one:
-      break;
-    default:
-      break;
-  }
-}
-''');
-  }
-
-  test_nullable_null() async {
-    await assertNoErrorsInCode('''
-enum E { one, two }
-
-void f(E? e) {
-  switch (e) {
-    case E.one:
-      break;
-    case E.two:
-      break;
-    case null:
-      break;
-  }
-}
-''');
-  }
-}
+class MissingEnumConstantInSwitchWithoutNullSafetyTest
+    extends PubPackageResolutionTest
+    with MissingEnumConstantInSwitchTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/mixin_of_non_class_test.dart b/pkg/analyzer/test/src/diagnostics/mixin_of_non_class_test.dart
index 53935facc73..47c9fd2ed0b 100644
--- a/pkg/analyzer/test/src/diagnostics/mixin_of_non_class_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/mixin_of_non_class_test.dart
@@ -10,13 +10,23 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(MixinOfNonClassTest);
-    defineReflectiveTests(MixinOfNonClassWithNullSafetyTest);
+    defineReflectiveTests(MixinOfNonClassWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class MixinOfNonClassTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with MixinOfNonClassTestCases {
+  test_Never() async {
+    await assertErrorsInCode('''
+class A with Never {}
+''', [
+      error(CompileTimeErrorCode.MIXIN_OF_NON_CLASS, 13, 5),
+    ]);
+  }
+}
+
+mixin MixinOfNonClassTestCases on PubPackageResolutionTest {
   test_class() async {
     await assertErrorsInCode(r'''
 int A = 7;
@@ -165,13 +175,5 @@ class C with p.M {}
 }
 
 @reflectiveTest
-class MixinOfNonClassWithNullSafetyTest extends MixinOfNonClassTest
-    with WithNullSafetyMixin {
-  test_Never() async {
-    await assertErrorsInCode('''
-class A with Never {}
-''', [
-      error(CompileTimeErrorCode.MIXIN_OF_NON_CLASS, 13, 5),
-    ]);
-  }
-}
+class MixinOfNonClassWithoutNullSafetyTest extends PubPackageResolutionTest
+    with MixinOfNonClassTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/mixin_super_class_constraint_non_interface_test.dart b/pkg/analyzer/test/src/diagnostics/mixin_super_class_constraint_non_interface_test.dart
index 204e6140f54..08db55e2ad2 100644
--- a/pkg/analyzer/test/src/diagnostics/mixin_super_class_constraint_non_interface_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/mixin_super_class_constraint_non_interface_test.dart
@@ -10,18 +10,12 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(MixinSuperClassConstraintNonInterfaceTest);
-    defineReflectiveTests(
-        MixinSuperClassConstraintNonInterfaceWithNullSafetyTest);
   });
 }
 
 @reflectiveTest
-class MixinSuperClassConstraintNonInterfaceTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {}
-
-@reflectiveTest
-class MixinSuperClassConstraintNonInterfaceWithNullSafetyTest
-    extends MixinSuperClassConstraintNonInterfaceTest with WithNullSafetyMixin {
+class MixinSuperClassConstraintNonInterfaceTest
+    extends PubPackageResolutionTest {
   test_Never() async {
     await assertErrorsInCode('''
 mixin M on Never {}
diff --git a/pkg/analyzer/test/src/diagnostics/non_constant_case_expression_test.dart b/pkg/analyzer/test/src/diagnostics/non_constant_case_expression_test.dart
index d36da7526c3..d77df25dfb5 100644
--- a/pkg/analyzer/test/src/diagnostics/non_constant_case_expression_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/non_constant_case_expression_test.dart
@@ -10,13 +10,15 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(NonConstantCaseExpressionTest);
-    defineReflectiveTests(NonConstantCaseExpressionWithNullSafetyTest);
+    defineReflectiveTests(NonConstantCaseExpressionWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class NonConstantCaseExpressionTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with NonConstantCaseExpressionTestCases {}
+
+mixin NonConstantCaseExpressionTestCases on PubPackageResolutionTest {
   test_constField() async {
     await assertNoErrorsInCode(r'''
 void f(C e) {
@@ -66,5 +68,6 @@ void f(var e) {
 }
 
 @reflectiveTest
-class NonConstantCaseExpressionWithNullSafetyTest
-    extends NonConstantCaseExpressionTest with WithNullSafetyMixin {}
+class NonConstantCaseExpressionWithoutNullSafetyTest
+    extends PubPackageResolutionTest
+    with NonConstantCaseExpressionTestCases, WithoutNullSafetyMixin {}
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 c0257146b2a..3c008f90f6e 100644
--- a/pkg/analyzer/test/src/diagnostics/not_map_spread_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/not_map_spread_test.dart
@@ -10,13 +10,13 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(NotMapSpreadTest);
-    defineReflectiveTests(NotMapSpreadNullSafetyTest);
+    defineReflectiveTests(NotMapSpreadWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
-class NotMapSpreadNullSafetyTest extends NotMapSpreadTest
-    with WithNullSafetyMixin {
+class NotMapSpreadTest extends PubPackageResolutionTest
+    with NotMapSpreadTestCases {
   test_map_typeParameter_bound_mapQuestion() async {
     await assertNoErrorsInCode('''
 void f<T extends Map<int, String>?>(T a) {
@@ -27,9 +27,7 @@ void f<T extends Map<int, String>?>(T a) {
   }
 }
 
-@reflectiveTest
-class NotMapSpreadTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+mixin NotMapSpreadTestCases on PubPackageResolutionTest {
   test_map() async {
     await assertNoErrorsInCode('''
 var a = {0: 0};
@@ -100,3 +98,7 @@ void f<T extends num>(T a) {
     ]);
   }
 }
+
+@reflectiveTest
+class NotMapSpreadWithoutNullSafetyTest extends PubPackageResolutionTest
+    with NotMapSpreadTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_from_catch_error_test.dart b/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_from_catch_error_test.dart
index 1e976ed871a..9a5d8e7d0cd 100644
--- a/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_from_catch_error_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/return_of_invalid_type_from_catch_error_test.dart
@@ -10,13 +10,46 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(ReturnOfInvalidTypeForCatchErrorTest);
-    defineReflectiveTests(ReturnOfInvalidTypeForCatchErrorWithNullSafetyTest);
+    defineReflectiveTests(
+        ReturnOfInvalidTypeForCatchErrorWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class ReturnOfInvalidTypeForCatchErrorTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with ReturnOfInvalidTypeForCatchErrorTestCases {
+  test_nullableType_emptyBody() async {
+    await assertNoErrorsInCode('''
+void f(Future<int?> future) {
+  future.catchError((e, st) {});
+}
+''');
+  }
+
+  test_nullableType_emptyReturn() async {
+    await assertErrorsInCode('''
+void f(Future<int?> future) {
+  future.catchError((e, st) {
+    return;
+  });
+}
+''', [
+      error(CompileTimeErrorCode.RETURN_WITHOUT_VALUE, 64, 6),
+    ]);
+  }
+
+  test_nullableType_invalidReturnType() async {
+    await assertErrorsInCode('''
+void f(Future<int?> future) {
+  future.catchError((e, st) => '');
+}
+''', [
+      error(HintCode.RETURN_OF_INVALID_TYPE_FROM_CATCH_ERROR, 61, 2),
+    ]);
+  }
+}
+
+mixin ReturnOfInvalidTypeForCatchErrorTestCases on PubPackageResolutionTest {
   test_async_okReturnType() async {
     await assertNoErrorsInCode('''
 void f(Future<int> future) {
@@ -167,35 +200,6 @@ void f(Future<int> future, void Function() g) {
 }
 
 @reflectiveTest
-class ReturnOfInvalidTypeForCatchErrorWithNullSafetyTest
-    extends ReturnOfInvalidTypeForCatchErrorTest with WithNullSafetyMixin {
-  test_nullableType_emptyBody() async {
-    await assertNoErrorsInCode('''
-void f(Future<int?> future) {
-  future.catchError((e, st) {});
-}
-''');
-  }
-
-  test_nullableType_emptyReturn() async {
-    await assertErrorsInCode('''
-void f(Future<int?> future) {
-  future.catchError((e, st) {
-    return;
-  });
-}
-''', [
-      error(CompileTimeErrorCode.RETURN_WITHOUT_VALUE, 64, 6),
-    ]);
-  }
-
-  test_nullableType_invalidReturnType() async {
-    await assertErrorsInCode('''
-void f(Future<int?> future) {
-  future.catchError((e, st) => '');
-}
-''', [
-      error(HintCode.RETURN_OF_INVALID_TYPE_FROM_CATCH_ERROR, 61, 2),
-    ]);
-  }
-}
+class ReturnOfInvalidTypeForCatchErrorWithoutNullSafetyTest
+    extends PubPackageResolutionTest
+    with ReturnOfInvalidTypeForCatchErrorTestCases, WithoutNullSafetyMixin {}
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 cfe890278ca..5f7f7cb33ea 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
@@ -11,13 +11,85 @@ main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(ReturnOfInvalidTypeTest);
     defineReflectiveTests(ReturnOfInvalidTypeWithNoImplicitCastsTest);
-    defineReflectiveTests(ReturnOfInvalidTypeWithNullSafetyTest);
+    defineReflectiveTests(ReturnOfInvalidTypeWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class ReturnOfInvalidTypeTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with ReturnOfInvalidTypeTestCases {
+  test_function_async_block_int__to_Future_void() async {
+    await assertErrorsInCode(r'''
+Future<void> f() async {
+  return 0;
+}
+''', [
+      error(CompileTimeErrorCode.RETURN_OF_INVALID_TYPE_FROM_FUNCTION, 34, 1),
+    ]);
+  }
+
+  test_function_async_block_void__to_Future_Null() async {
+    await assertErrorsInCode(r'''
+Future<Null> f(void a) async {
+  return a;
+}
+''', [
+      error(CompileTimeErrorCode.RETURN_OF_INVALID_TYPE_FROM_FUNCTION, 40, 1),
+    ]);
+  }
+
+  test_function_async_block_void__to_FutureOr_ObjectQ() async {
+    await assertErrorsInCode(r'''
+import 'dart:async';
+
+FutureOr<Object?> f(void a) async {
+  return a;
+}
+''', [
+      error(CompileTimeErrorCode.RETURN_OF_INVALID_TYPE_FROM_FUNCTION, 67, 1),
+    ]);
+  }
+
+  test_function_async_expression_dynamic__to_Future_int() async {
+    await assertNoErrorsInCode(r'''
+Future<int> f(dynamic a) async => a;
+''');
+  }
+
+  test_functionExpression_async_futureOr_void__to_Object() async {
+    await assertNoErrorsInCode(r'''
+void a = null;
+
+Object Function() f = () async {
+  return a;
+};
+''');
+  }
+
+  test_functionExpression_async_futureQ_void__to_Object() async {
+    await assertNoErrorsInCode(r'''
+Future<void>? a = (throw 0);
+
+Object Function() f = () async {
+  return a;
+};
+''');
+  }
+
+  test_functionExpression_async_void__to_FutureOr_ObjectQ() async {
+    await assertNoErrorsInCode(r'''
+import 'dart:async';
+
+void a = (throw 0);
+
+FutureOr<Object?> Function() f = () async {
+  return a;
+};
+''');
+  }
+}
+
+mixin ReturnOfInvalidTypeTestCases on PubPackageResolutionTest {
   test_closure() async {
     await assertErrorsInCode('''
 typedef Td = int Function();
@@ -415,75 +487,5 @@ Future<List<String>> f() async {
 }
 
 @reflectiveTest
-class ReturnOfInvalidTypeWithNullSafetyTest extends ReturnOfInvalidTypeTest
-    with WithNullSafetyMixin {
-  test_function_async_block_int__to_Future_void() async {
-    await assertErrorsInCode(r'''
-Future<void> f() async {
-  return 0;
-}
-''', [
-      error(CompileTimeErrorCode.RETURN_OF_INVALID_TYPE_FROM_FUNCTION, 34, 1),
-    ]);
-  }
-
-  test_function_async_block_void__to_Future_Null() async {
-    await assertErrorsInCode(r'''
-Future<Null> f(void a) async {
-  return a;
-}
-''', [
-      error(CompileTimeErrorCode.RETURN_OF_INVALID_TYPE_FROM_FUNCTION, 40, 1),
-    ]);
-  }
-
-  test_function_async_block_void__to_FutureOr_ObjectQ() async {
-    await assertErrorsInCode(r'''
-import 'dart:async';
-
-FutureOr<Object?> f(void a) async {
-  return a;
-}
-''', [
-      error(CompileTimeErrorCode.RETURN_OF_INVALID_TYPE_FROM_FUNCTION, 67, 1),
-    ]);
-  }
-
-  test_function_async_expression_dynamic__to_Future_int() async {
-    await assertNoErrorsInCode(r'''
-Future<int> f(dynamic a) async => a;
-''');
-  }
-
-  test_functionExpression_async_futureOr_void__to_Object() async {
-    await assertNoErrorsInCode(r'''
-void a = null;
-
-Object Function() f = () async {
-  return a;
-};
-''');
-  }
-
-  test_functionExpression_async_futureQ_void__to_Object() async {
-    await assertNoErrorsInCode(r'''
-Future<void>? a = (throw 0);
-
-Object Function() f = () async {
-  return a;
-};
-''');
-  }
-
-  test_functionExpression_async_void__to_FutureOr_ObjectQ() async {
-    await assertNoErrorsInCode(r'''
-import 'dart:async';
-
-void a = (throw 0);
-
-FutureOr<Object?> Function() f = () async {
-  return a;
-};
-''');
-  }
-}
+class ReturnOfInvalidTypeWithoutNullSafetyTest extends PubPackageResolutionTest
+    with ReturnOfInvalidTypeTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/return_type_invalid_for_catch_error_test.dart b/pkg/analyzer/test/src/diagnostics/return_type_invalid_for_catch_error_test.dart
index fd534d0849a..b5a19e87c71 100644
--- a/pkg/analyzer/test/src/diagnostics/return_type_invalid_for_catch_error_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/return_type_invalid_for_catch_error_test.dart
@@ -10,13 +10,25 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(ReturnTypeInvalidForCatchErrorTest);
-    defineReflectiveTests(ReturnTypeInvalidForCatchErrorWithNullSafetyTest);
+    defineReflectiveTests(ReturnTypeInvalidForCatchErrorWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class ReturnTypeInvalidForCatchErrorTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with ReturnTypeInvalidForCatchErrorTestCases {
+  test_nullableReturnType() async {
+    await assertErrorsInCode('''
+void f(Future<int> future, String? Function(dynamic, StackTrace) cb) {
+  future.catchError(cb);
+}
+''', [
+      error(HintCode.RETURN_TYPE_INVALID_FOR_CATCH_ERROR, 91, 2),
+    ]);
+  }
+}
+
+mixin ReturnTypeInvalidForCatchErrorTestCases on PubPackageResolutionTest {
   test_dynamic_returnTypeIsUnrelatedFuture() async {
     await assertNoErrorsInCode('''
 void f(
@@ -87,15 +99,6 @@ void f(Future<void> future, String Function(dynamic, StackTrace) cb) {
 }
 
 @reflectiveTest
-class ReturnTypeInvalidForCatchErrorWithNullSafetyTest
-    extends ReturnTypeInvalidForCatchErrorTest with WithNullSafetyMixin {
-  test_nullableReturnType() async {
-    await assertErrorsInCode('''
-void f(Future<int> future, String? Function(dynamic, StackTrace) cb) {
-  future.catchError(cb);
-}
-''', [
-      error(HintCode.RETURN_TYPE_INVALID_FOR_CATCH_ERROR, 91, 2),
-    ]);
-  }
-}
+class ReturnTypeInvalidForCatchErrorWithoutNullSafetyTest
+    extends PubPackageResolutionTest
+    with ReturnTypeInvalidForCatchErrorTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/return_without_value_test.dart b/pkg/analyzer/test/src/diagnostics/return_without_value_test.dart
index f90e7e6f502..b6149bb18a1 100644
--- a/pkg/analyzer/test/src/diagnostics/return_without_value_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/return_without_value_test.dart
@@ -10,13 +10,15 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(ReturnWithoutValueTest);
-    defineReflectiveTests(ReturnWithoutValueWithNullSafetyTest);
+    defineReflectiveTests(ReturnWithoutValueWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class ReturnWithoutValueTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with ReturnWithoutValueTestCases {}
+
+mixin ReturnWithoutValueTestCases on PubPackageResolutionTest {
   test_async_futureInt() async {
     await assertErrorsInCode('''
 Future<int> f() async {
@@ -163,5 +165,5 @@ int f(int x) {
 }
 
 @reflectiveTest
-class ReturnWithoutValueWithNullSafetyTest extends ReturnWithoutValueTest
-    with WithNullSafetyMixin {}
+class ReturnWithoutValueWithoutNullSafetyTest extends PubPackageResolutionTest
+    with ReturnWithoutValueTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/sdk_version_never_test.dart b/pkg/analyzer/test/src/diagnostics/sdk_version_never_test.dart
index 4773eaeda45..ad2aa2d1f25 100644
--- a/pkg/analyzer/test/src/diagnostics/sdk_version_never_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/sdk_version_never_test.dart
@@ -11,25 +11,12 @@ import 'sdk_constraint_verifier_support.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(SdkVersionNeverTest);
-    defineReflectiveTests(SdkVersionNeverWithNullSafetyTest);
+    defineReflectiveTests(SdkVersionNeverWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
-class SdkVersionNeverTest extends SdkConstraintVerifierTest
-    with WithoutNullSafetyMixin {
-  test_languageVersionBeforeNullSafety() async {
-    await verifyVersion('2.7.0', r'''
-Never foo;
-''', expectedErrors: [
-      error(HintCode.SDK_VERSION_NEVER, 0, 5),
-    ]);
-  }
-}
-
-@reflectiveTest
-class SdkVersionNeverWithNullSafetyTest extends SdkConstraintVerifierTest
-    with WithNullSafetyMixin {
+class SdkVersionNeverTest extends SdkConstraintVerifierTest {
   test_experimentEnabled() async {
     await verifyVersion('2.7.0', r'''
 Never foo = (throw 42);
@@ -45,3 +32,15 @@ Never foo = (throw 42);
     ]);
   }
 }
+
+@reflectiveTest
+class SdkVersionNeverWithoutNullSafetyTest extends SdkConstraintVerifierTest
+    with WithoutNullSafetyMixin {
+  test_languageVersionBeforeNullSafety() async {
+    await verifyVersion('2.7.0', r'''
+Never foo;
+''', expectedErrors: [
+      error(HintCode.SDK_VERSION_NEVER, 0, 5),
+    ]);
+  }
+}
diff --git a/pkg/analyzer/test/src/diagnostics/type_parameter_supertype_of_its_bound_test.dart b/pkg/analyzer/test/src/diagnostics/type_parameter_supertype_of_its_bound_test.dart
index 001d9470a86..fdfa18277cc 100644
--- a/pkg/analyzer/test/src/diagnostics/type_parameter_supertype_of_its_bound_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/type_parameter_supertype_of_its_bound_test.dart
@@ -10,13 +10,16 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(TypeParameterSupertypeOfItsBoundTest);
-    defineReflectiveTests(TypeParameterSupertypeOfItsBoundWithNullSafetyTest);
+    defineReflectiveTests(
+        TypeParameterSupertypeOfItsBoundWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class TypeParameterSupertypeOfItsBoundTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with TypeParameterSupertypeOfItsBoundTestCases {}
+
+mixin TypeParameterSupertypeOfItsBoundTestCases on PubPackageResolutionTest {
   test_1of1() async {
     await assertErrorsInCode(r'''
 class A<T extends T> {
@@ -50,5 +53,6 @@ class A<T1 extends T3, T2, T3 extends T1> {
 }
 
 @reflectiveTest
-class TypeParameterSupertypeOfItsBoundWithNullSafetyTest
-    extends TypeParameterSupertypeOfItsBoundTest with WithNullSafetyMixin {}
+class TypeParameterSupertypeOfItsBoundWithoutNullSafetyTest
+    extends PubPackageResolutionTest
+    with TypeParameterSupertypeOfItsBoundTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/undefined_hidden_name_test.dart b/pkg/analyzer/test/src/diagnostics/undefined_hidden_name_test.dart
index 6fcfad309a7..cf1eba2b94b 100644
--- a/pkg/analyzer/test/src/diagnostics/undefined_hidden_name_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/undefined_hidden_name_test.dart
@@ -10,13 +10,15 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UndefinedHiddenNameTest);
-    defineReflectiveTests(UndefinedHiddenNameWithNullSafetyTest);
+    defineReflectiveTests(UndefinedHiddenNameWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class UndefinedHiddenNameTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with UndefinedHiddenNameTestCases {}
+
+mixin UndefinedHiddenNameTestCases on PubPackageResolutionTest {
   test_export() async {
     newFile('$testPackageLibPath/lib1.dart');
     await assertErrorsInCode(r'''
@@ -38,5 +40,5 @@ import 'lib1.dart' hide a;
 }
 
 @reflectiveTest
-class UndefinedHiddenNameWithNullSafetyTest extends UndefinedHiddenNameTest
-    with WithNullSafetyMixin {}
+class UndefinedHiddenNameWithoutNullSafetyTest extends PubPackageResolutionTest
+    with UndefinedHiddenNameTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/undefined_identifier_test.dart b/pkg/analyzer/test/src/diagnostics/undefined_identifier_test.dart
index 2b0b5a5c3ab..c339039bf98 100644
--- a/pkg/analyzer/test/src/diagnostics/undefined_identifier_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/undefined_identifier_test.dart
@@ -11,13 +11,38 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UndefinedIdentifierTest);
-    defineReflectiveTests(UndefinedIdentifierWithNullSafetyTest);
+    defineReflectiveTests(UndefinedIdentifierWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class UndefinedIdentifierTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with UndefinedIdentifierTestCases {
+  test_get_from_external_variable_final_valid() async {
+    await assertNoErrorsInCode('''
+external final int x;
+int f() => x;
+''');
+  }
+
+  test_get_from_external_variable_valid() async {
+    await assertNoErrorsInCode('''
+external int x;
+int f() => x;
+''');
+  }
+
+  test_set_external_variable_valid() async {
+    await assertNoErrorsInCode('''
+external int x;
+void f(int value) {
+  x = value;
+}
+''');
+  }
+}
+
+mixin UndefinedIdentifierTestCases on PubPackageResolutionTest {
   test_annotation_favors_scope_resolution_over_this_resolution_class() async {
     // If an annotation on a class type parameter cannot be resolved using the
     // normal scope resolution mechanism, it is resolved via implicit `this`.
@@ -397,28 +422,5 @@ void f(int p) {
 }
 
 @reflectiveTest
-class UndefinedIdentifierWithNullSafetyTest extends UndefinedIdentifierTest
-    with WithNullSafetyMixin {
-  test_get_from_external_variable_final_valid() async {
-    await assertNoErrorsInCode('''
-external final int x;
-int f() => x;
-''');
-  }
-
-  test_get_from_external_variable_valid() async {
-    await assertNoErrorsInCode('''
-external int x;
-int f() => x;
-''');
-  }
-
-  test_set_external_variable_valid() async {
-    await assertNoErrorsInCode('''
-external int x;
-void f(int value) {
-  x = value;
-}
-''');
-  }
-}
+class UndefinedIdentifierWithoutNullSafetyTest extends PubPackageResolutionTest
+    with UndefinedIdentifierTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/undefined_shown_name_test.dart b/pkg/analyzer/test/src/diagnostics/undefined_shown_name_test.dart
index ea89f9a3652..f486367ac00 100644
--- a/pkg/analyzer/test/src/diagnostics/undefined_shown_name_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/undefined_shown_name_test.dart
@@ -10,13 +10,15 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UndefinedShownNameTest);
-    defineReflectiveTests(UndefinedShownNameWithNullSafetyTest);
+    defineReflectiveTests(UndefinedShownNameWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class UndefinedShownNameTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with UndefinedShownNameTestCases {}
+
+mixin UndefinedShownNameTestCases on PubPackageResolutionTest {
   test_export() async {
     newFile('$testPackageLibPath/lib1.dart');
     await assertErrorsInCode(r'''
@@ -38,5 +40,5 @@ import 'lib1.dart' show a;
 }
 
 @reflectiveTest
-class UndefinedShownNameWithNullSafetyTest extends UndefinedShownNameTest
-    with WithNullSafetyMixin {}
+class UndefinedShownNameWithoutNullSafetyTest extends PubPackageResolutionTest
+    with UndefinedShownNameTestCases, WithoutNullSafetyMixin {}
diff --git a/pkg/analyzer/test/src/diagnostics/unnecessary_type_check_test.dart b/pkg/analyzer/test/src/diagnostics/unnecessary_type_check_test.dart
index 65e5479c96b..fef92e86e1d 100644
--- a/pkg/analyzer/test/src/diagnostics/unnecessary_type_check_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/unnecessary_type_check_test.dart
@@ -10,15 +10,36 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(UnnecessaryTypeCheckFalseTest);
-    defineReflectiveTests(UnnecessaryTypeCheckFalseWithNullSafetyTest);
+    defineReflectiveTests(UnnecessaryTypeCheckFalseWithoutNullSafetyTest);
     defineReflectiveTests(UnnecessaryTypeCheckTrueTest);
-    defineReflectiveTests(UnnecessaryTypeCheckTrueWithNullSafetyTest);
+    defineReflectiveTests(UnnecessaryTypeCheckTrueWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class UnnecessaryTypeCheckFalseTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with UnnecessaryTypeCheckFalseTestCases {
+  @override
+  test_type_not_object() async {
+    await assertNoErrorsInCode(r'''
+void f<T>(T a) {
+  a is! Object;
+}
+''');
+  }
+
+  test_type_not_objectQuestion() async {
+    await assertErrorsInCode(r'''
+void f<T>(T a) {
+  a is! Object?;
+}
+''', [
+      error(HintCode.UNNECESSARY_TYPE_CHECK_FALSE, 19, 13),
+    ]);
+  }
+}
+
+mixin UnnecessaryTypeCheckFalseTestCases on PubPackageResolutionTest {
   test_null_not_Null() async {
     await assertErrorsInCode(r'''
 var b = null is! Null;
@@ -49,31 +70,34 @@ void f<T>(T a) {
 }
 
 @reflectiveTest
-class UnnecessaryTypeCheckFalseWithNullSafetyTest
-    extends UnnecessaryTypeCheckFalseTest with WithNullSafetyMixin {
+class UnnecessaryTypeCheckFalseWithoutNullSafetyTest
+    extends PubPackageResolutionTest
+    with UnnecessaryTypeCheckFalseTestCases, WithoutNullSafetyMixin {}
+
+@reflectiveTest
+class UnnecessaryTypeCheckTrueTest extends PubPackageResolutionTest
+    with UnnecessaryTypeCheckTrueTestCases {
   @override
-  test_type_not_object() async {
+  test_type_is_object() async {
     await assertNoErrorsInCode(r'''
 void f<T>(T a) {
-  a is! Object;
+  a is Object;
 }
 ''');
   }
 
-  test_type_not_objectQuestion() async {
+  test_type_is_objectQuestion() async {
     await assertErrorsInCode(r'''
 void f<T>(T a) {
-  a is! Object?;
+  a is Object?;
 }
 ''', [
-      error(HintCode.UNNECESSARY_TYPE_CHECK_FALSE, 19, 13),
+      error(HintCode.UNNECESSARY_TYPE_CHECK_TRUE, 19, 12),
     ]);
   }
 }
 
-@reflectiveTest
-class UnnecessaryTypeCheckTrueTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+mixin UnnecessaryTypeCheckTrueTestCases on PubPackageResolutionTest {
   test_null_is_Null() async {
     await assertErrorsInCode(r'''
 var b = null is Null;
@@ -104,24 +128,6 @@ void f<T>(T a) {
 }
 
 @reflectiveTest
-class UnnecessaryTypeCheckTrueWithNullSafetyTest
-    extends UnnecessaryTypeCheckTrueTest with WithNullSafetyMixin {
-  @override
-  test_type_is_object() async {
-    await assertNoErrorsInCode(r'''
-void f<T>(T a) {
-  a is Object;
-}
-''');
-  }
-
-  test_type_is_objectQuestion() async {
-    await assertErrorsInCode(r'''
-void f<T>(T a) {
-  a is Object?;
-}
-''', [
-      error(HintCode.UNNECESSARY_TYPE_CHECK_TRUE, 19, 12),
-    ]);
-  }
-}
+class UnnecessaryTypeCheckTrueWithoutNullSafetyTest
+    extends PubPackageResolutionTest
+    with UnnecessaryTypeCheckTrueTestCases, WithoutNullSafetyMixin {}
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 072b7337943..ddb8c9ce124 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
@@ -10,13 +10,15 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(YieldOfInvalidTypeTest);
-    defineReflectiveTests(YieldOfInvalidTypeWithNullSafetyTest);
+    defineReflectiveTests(YieldOfInvalidTypeWithoutNullSafetyTest);
   });
 }
 
 @reflectiveTest
 class YieldOfInvalidTypeTest extends PubPackageResolutionTest
-    with WithoutNullSafetyMixin {
+    with YieldOfInvalidTypeTestCases {}
+
+mixin YieldOfInvalidTypeTestCases on PubPackageResolutionTest {
   test_none_asyncStar_dynamic_to_streamInt() async {
     await assertErrorsInCode(
         '''
@@ -448,5 +450,5 @@ Iterable<String> g() => throw 0;
 }
 
 @reflectiveTest
-class YieldOfInvalidTypeWithNullSafetyTest extends YieldOfInvalidTypeTest
-    with WithNullSafetyMixin {}
+class YieldOfInvalidTypeWithoutNullSafetyTest extends PubPackageResolutionTest
+    with YieldOfInvalidTypeTestCases, WithoutNullSafetyMixin {}