diff --git a/tests/corelib/map_test.dart b/tests/corelib/map_test.dart
index 30618b09357..ecc12173b85 100644
--- a/tests/corelib/map_test.dart
+++ b/tests/corelib/map_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library map_test;
 
 import "package:expect/expect.dart";
diff --git a/tests/corelib/map_update_test.dart b/tests/corelib/map_update_test.dart
index 1893a1b01d7..0f9fe0dcd73 100644
--- a/tests/corelib/map_update_test.dart
+++ b/tests/corelib/map_update_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 import 'dart:collection';
 import 'dart:convert' show json;
diff --git a/tests/language/abstract/getter2_test.dart b/tests/language/abstract/getter2_test.dart
index e1240c5a276..69a70f38778 100644
--- a/tests/language/abstract/getter2_test.dart
+++ b/tests/language/abstract/getter2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class A {
diff --git a/tests/language/call/method_as_cast_test.dart b/tests/language/call/method_as_cast_test.dart
index 48ae3b70278..cda6967a199 100644
--- a/tests/language/call/method_as_cast_test.dart
+++ b/tests/language/call/method_as_cast_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_instance_test.dart b/tests/language/call/method_implicit_invoke_instance_test.dart
index fdcb12b66e7..5aaba820532 100644
--- a/tests/language/call/method_implicit_invoke_instance_test.dart
+++ b/tests/language/call/method_implicit_invoke_instance_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_local_runtime_1_test.dart b/tests/language/call/method_implicit_invoke_local_runtime_1_test.dart
index 5df9be06d50..7a43be60b26 100644
--- a/tests/language/call/method_implicit_invoke_local_runtime_1_test.dart
+++ b/tests/language/call/method_implicit_invoke_local_runtime_1_test.dart
@@ -4,6 +4,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_local_runtime_2_test.dart b/tests/language/call/method_implicit_invoke_local_runtime_2_test.dart
index b4b00f4a855..7b50fcf0b6d 100644
--- a/tests/language/call/method_implicit_invoke_local_runtime_2_test.dart
+++ b/tests/language/call/method_implicit_invoke_local_runtime_2_test.dart
@@ -4,6 +4,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_local_runtime_3_test.dart b/tests/language/call/method_implicit_invoke_local_runtime_3_test.dart
index 215d9981b1c..362c19fac95 100644
--- a/tests/language/call/method_implicit_invoke_local_runtime_3_test.dart
+++ b/tests/language/call/method_implicit_invoke_local_runtime_3_test.dart
@@ -4,6 +4,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_local_runtime_4_test.dart b/tests/language/call/method_implicit_invoke_local_runtime_4_test.dart
index 01a364c9a68..680f8b19089 100644
--- a/tests/language/call/method_implicit_invoke_local_runtime_4_test.dart
+++ b/tests/language/call/method_implicit_invoke_local_runtime_4_test.dart
@@ -4,6 +4,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_local_runtime_test.dart b/tests/language/call/method_implicit_invoke_local_runtime_test.dart
index f06206fa497..12a0d80d4d8 100644
--- a/tests/language/call/method_implicit_invoke_local_runtime_test.dart
+++ b/tests/language/call/method_implicit_invoke_local_runtime_test.dart
@@ -4,6 +4,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_local_test.dart b/tests/language/call/method_implicit_invoke_local_test.dart
index 3950e1bd3e5..fd959fdea17 100644
--- a/tests/language/call/method_implicit_invoke_local_test.dart
+++ b/tests/language/call/method_implicit_invoke_local_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_static_test.dart b/tests/language/call/method_implicit_invoke_static_test.dart
index 17f868d2aa9..b299dcc3850 100644
--- a/tests/language/call/method_implicit_invoke_static_test.dart
+++ b/tests/language/call/method_implicit_invoke_static_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_implicit_invoke_top_level_test.dart b/tests/language/call/method_implicit_invoke_top_level_test.dart
index eaed546ffab..af1ba94c866 100644
--- a/tests/language/call/method_implicit_invoke_top_level_test.dart
+++ b/tests/language/call/method_implicit_invoke_top_level_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/call/method_is_check_test.dart b/tests/language/call/method_is_check_test.dart
index 9c705a3a032..a8eb2b82750 100644
--- a/tests/language/call/method_is_check_test.dart
+++ b/tests/language/call/method_is_check_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program to test arithmetic operations.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/class/override_inference_test.dart b/tests/language/class/override_inference_test.dart
index 00575945042..cbfd12be332 100644
--- a/tests/language/class/override_inference_test.dart
+++ b/tests/language/class/override_inference_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that inheriting types on overriding members work as specified.
 
 // ignore_for_file: unused_local_variable
diff --git a/tests/language/const/constructor_mixin2_test.dart b/tests/language/const/constructor_mixin2_test.dart
index 873141d853b..6bd72d6bd0e 100644
--- a/tests/language/const/constructor_mixin2_test.dart
+++ b/tests/language/const/constructor_mixin2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class Mixin {
   var nonFinalField;
 }
diff --git a/tests/language/const/constructor_mixin3_test.dart b/tests/language/const/constructor_mixin3_test.dart
index 9eb4d760830..0cb3206734b 100644
--- a/tests/language/const/constructor_mixin3_test.dart
+++ b/tests/language/const/constructor_mixin3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class Mixin {}
 
 class A {
diff --git a/tests/language/const/constructor_mixin_test.dart b/tests/language/const/constructor_mixin_test.dart
index a177ce14ae5..c7ea4743319 100644
--- a/tests/language/const/constructor_mixin_test.dart
+++ b/tests/language/const/constructor_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class Mixin {}
 
 class A {
diff --git a/tests/language/constructor/missing_initializer_test.dart b/tests/language/constructor/missing_initializer_test.dart
index 2de088e356e..ff46aae59b5 100644
--- a/tests/language/constructor/missing_initializer_test.dart
+++ b/tests/language/constructor/missing_initializer_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that it is an error for a class with no generative constructors to
 // have a final instance variable without an initializing expression, except
 // if it is `abstract` or `external`. The latter also holds in a class with
diff --git a/tests/language/constructor/with_mixin_test.dart b/tests/language/constructor/with_mixin_test.dart
index 5e4badcb633..d3d0915d872 100644
--- a/tests/language/constructor/with_mixin_test.dart
+++ b/tests/language/constructor/with_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test super constructor invocation with mixins.
 // Regression test for issue dartbug.com/22604
 
diff --git a/tests/language/covariant/setter_test.dart b/tests/language/covariant/setter_test.dart
index 1a19dcac57e..af108261250 100644
--- a/tests/language/covariant/setter_test.dart
+++ b/tests/language/covariant/setter_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class A {}
diff --git a/tests/language/covariant/subtyping_test.dart b/tests/language/covariant/subtyping_test.dart
index 43d665e737b..507f5c3d22a 100644
--- a/tests/language/covariant/subtyping_test.dart
+++ b/tests/language/covariant/subtyping_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class Fields<T> {
diff --git a/tests/language/covariant/subtyping_with_mixin_test.dart b/tests/language/covariant/subtyping_with_mixin_test.dart
index 8bff28edae6..eee707ea875 100644
--- a/tests/language/covariant/subtyping_with_mixin_test.dart
+++ b/tests/language/covariant/subtyping_with_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class A {}
diff --git a/tests/language/covariant_override/tear_off_type_test.dart b/tests/language/covariant_override/tear_off_type_test.dart
index bd1012b5923..06b0cc632ec 100644
--- a/tests/language/covariant_override/tear_off_type_test.dart
+++ b/tests/language/covariant_override/tear_off_type_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 // If a parameter is directly or indirectly a covariant override, its type in
diff --git a/tests/language/deferred/inheritance_constraints_runtime_test.dart b/tests/language/deferred/inheritance_constraints_runtime_test.dart
index 719a170a8e6..b6e9a2250c7 100644
--- a/tests/language/deferred/inheritance_constraints_runtime_test.dart
+++ b/tests/language/deferred/inheritance_constraints_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 import "inheritance_constraints_lib.dart" deferred as lib;
 
diff --git a/tests/language/deferred/mixin_test.dart b/tests/language/deferred/mixin_test.dart
index 33594b71de4..f644b327431 100644
--- a/tests/language/deferred/mixin_test.dart
+++ b/tests/language/deferred/mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 import 'package:async_helper/async_helper.dart';
 
diff --git a/tests/language/generic/constructor_mixin2_runtime_test.dart b/tests/language/generic/constructor_mixin2_runtime_test.dart
index 3c44d0ca1d4..576dcac04c9 100644
--- a/tests/language/generic/constructor_mixin2_runtime_test.dart
+++ b/tests/language/generic/constructor_mixin2_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
diff --git a/tests/language/generic/constructor_mixin2_test.dart b/tests/language/generic/constructor_mixin2_test.dart
index a98846a55c4..4cba565b4ab 100644
--- a/tests/language/generic/constructor_mixin2_test.dart
+++ b/tests/language/generic/constructor_mixin2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
diff --git a/tests/language/generic/constructor_mixin3_runtime_test.dart b/tests/language/generic/constructor_mixin3_runtime_test.dart
index 9098eff06d1..b33fbb765bf 100644
--- a/tests/language/generic/constructor_mixin3_runtime_test.dart
+++ b/tests/language/generic/constructor_mixin3_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
diff --git a/tests/language/generic/constructor_mixin3_test.dart b/tests/language/generic/constructor_mixin3_test.dart
index e51e0cb11a7..d20fa6f2d31 100644
--- a/tests/language/generic/constructor_mixin3_test.dart
+++ b/tests/language/generic/constructor_mixin3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
diff --git a/tests/language/generic/constructor_mixin_runtime_test.dart b/tests/language/generic/constructor_mixin_runtime_test.dart
index a0425f5c749..7a33dba872a 100644
--- a/tests/language/generic/constructor_mixin_runtime_test.dart
+++ b/tests/language/generic/constructor_mixin_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
diff --git a/tests/language/generic/constructor_mixin_test.dart b/tests/language/generic/constructor_mixin_test.dart
index 015b0522475..2b234cd3c35 100644
--- a/tests/language/generic/constructor_mixin_test.dart
+++ b/tests/language/generic/constructor_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that parameter types are checked correctly in the face of
 // mixin application upon a generic constructor.
 
diff --git a/tests/language/generic/field_mixin2_test.dart b/tests/language/generic/field_mixin2_test.dart
index 99e2d926a8e..b318b1c1d72 100644
--- a/tests/language/generic/field_mixin2_test.dart
+++ b/tests/language/generic/field_mixin2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/generic/field_mixin3_test.dart b/tests/language/generic/field_mixin3_test.dart
index d8e78f3217f..972b2592f25 100644
--- a/tests/language/generic/field_mixin3_test.dart
+++ b/tests/language/generic/field_mixin3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/generic/field_mixin4_test.dart b/tests/language/generic/field_mixin4_test.dart
index 137fa1bd1ed..d27e1daecec 100644
--- a/tests/language/generic/field_mixin4_test.dart
+++ b/tests/language/generic/field_mixin4_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/generic/field_mixin5_test.dart b/tests/language/generic/field_mixin5_test.dart
index a684903b361..9a3b4157691 100644
--- a/tests/language/generic/field_mixin5_test.dart
+++ b/tests/language/generic/field_mixin5_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/generic/field_mixin6_runtime_test.dart b/tests/language/generic/field_mixin6_runtime_test.dart
index 7fa746bd41e..25a2f7b628c 100644
--- a/tests/language/generic/field_mixin6_runtime_test.dart
+++ b/tests/language/generic/field_mixin6_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/generic/field_mixin6_test.dart b/tests/language/generic/field_mixin6_test.dart
index 303df88354b..b8cd526d028 100644
--- a/tests/language/generic/field_mixin6_test.dart
+++ b/tests/language/generic/field_mixin6_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/generic/field_mixin_test.dart b/tests/language/generic/field_mixin_test.dart
index ea34a9e2d0e..daf17e3181c 100644
--- a/tests/language/generic/field_mixin_test.dart
+++ b/tests/language/generic/field_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that generic types in mixins are handled.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/generic/instanceof5_test.dart b/tests/language/generic/instanceof5_test.dart
index 5df4087d3ce..70b206a4f48 100644
--- a/tests/language/generic/instanceof5_test.dart
+++ b/tests/language/generic/instanceof5_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that instanceof works correctly with type variables.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/generic/method_types_test.dart b/tests/language/generic/method_types_test.dart
index 2e2ee9e5e17..5cecf756e8e 100644
--- a/tests/language/generic/method_types_test.dart
+++ b/tests/language/generic/method_types_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 typedef Convert1<O> = O Function<I>(I input);
diff --git a/tests/language/malformed/inheritance_test.dart b/tests/language/malformed/inheritance_test.dart
index 4161dfab2fd..8c2aaba59ea 100644
--- a/tests/language/malformed/inheritance_test.dart
+++ b/tests/language/malformed/inheritance_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Tests that malformed types used in extends, implements, and with clauses
 // cause compile-time errors.
 
diff --git a/tests/language/mixin/abstract_getter_test.dart b/tests/language/mixin/abstract_getter_test.dart
index 7fe7bd92363..65707d2a86f 100644
--- a/tests/language/mixin/abstract_getter_test.dart
+++ b/tests/language/mixin/abstract_getter_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 abstract class B {
diff --git a/tests/language/mixin/accessor_test.dart b/tests/language/mixin/accessor_test.dart
index bb346e8d876..d19545a3f77 100644
--- a/tests/language/mixin/accessor_test.dart
+++ b/tests/language/mixin/accessor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test case for DDC bug where if a getter/setter is mixed in
 // without a corresponding getter/setter, DDC fails to install a the
 // corresponding getter/setter that calls super.
diff --git a/tests/language/mixin/and_extension_member_test.dart b/tests/language/mixin/and_extension_member_test.dart
index 3f96a4a6d7a..f1b336c65e0 100644
--- a/tests/language/mixin/and_extension_member_test.dart
+++ b/tests/language/mixin/and_extension_member_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'dart:collection';
 import 'package:expect/expect.dart';
 
diff --git a/tests/language/mixin/black_listed_test.dart b/tests/language/mixin/black_listed_test.dart
index 08ff386d3e2..d11c910f26b 100644
--- a/tests/language/mixin/black_listed_test.dart
+++ b/tests/language/mixin/black_listed_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Check mixin of black-listed types.
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/mixin/bound_test.dart b/tests/language/mixin/bound_test.dart
index 23b4e29ab0f..eab972d9254 100644
--- a/tests/language/mixin/bound_test.dart
+++ b/tests/language/mixin/bound_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 // library abstract_expressions;
diff --git a/tests/language/mixin/cyclic_runtime_test.dart b/tests/language/mixin/cyclic_runtime_test.dart
index 2217ac172f4..9ddf4449c23 100644
--- a/tests/language/mixin/cyclic_runtime_test.dart
+++ b/tests/language/mixin/cyclic_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test for cyclicity check on named mixin applications.
 
 class A<T> {}
diff --git a/tests/language/mixin/cyclic_test.dart b/tests/language/mixin/cyclic_test.dart
index e128af7cefd..f1dac690bcd 100644
--- a/tests/language/mixin/cyclic_test.dart
+++ b/tests/language/mixin/cyclic_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test for cyclicity check on named mixin applications.
 
 class A<T> {}
diff --git a/tests/language/mixin/extends_field_test.dart b/tests/language/mixin/extends_field_test.dart
index 778a2421397..aa6c50d31f8 100644
--- a/tests/language/mixin/extends_field_test.dart
+++ b/tests/language/mixin/extends_field_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {
diff --git a/tests/language/mixin/extends_is_test.dart b/tests/language/mixin/extends_is_test.dart
index 5c3a1c310e2..01c1c9f9e43 100644
--- a/tests/language/mixin/extends_is_test.dart
+++ b/tests/language/mixin/extends_is_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {}
diff --git a/tests/language/mixin/extends_method_test.dart b/tests/language/mixin/extends_method_test.dart
index cee3d657e03..55ddc481a7c 100644
--- a/tests/language/mixin/extends_method_test.dart
+++ b/tests/language/mixin/extends_method_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {
diff --git a/tests/language/mixin/factory_constructor_test.dart b/tests/language/mixin/factory_constructor_test.dart
index ac0e22762d5..0be7643f19b 100644
--- a/tests/language/mixin/factory_constructor_test.dart
+++ b/tests/language/mixin/factory_constructor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Base {
diff --git a/tests/language/mixin/field_initializer_test.dart b/tests/language/mixin/field_initializer_test.dart
index e2855fe746f..b3e777d1ee0 100644
--- a/tests/language/mixin/field_initializer_test.dart
+++ b/tests/language/mixin/field_initializer_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test program for testing throw statement
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/mixin/field_test.dart b/tests/language/mixin/field_test.dart
index bd821ce54a3..e8b243cffa2 100644
--- a/tests/language/mixin/field_test.dart
+++ b/tests/language/mixin/field_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {
diff --git a/tests/language/mixin/forwarding_constructor1_test.dart b/tests/language/mixin/forwarding_constructor1_test.dart
index b0e97ab7af2..b41046aff55 100644
--- a/tests/language/mixin/forwarding_constructor1_test.dart
+++ b/tests/language/mixin/forwarding_constructor1_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin1 {
diff --git a/tests/language/mixin/forwarding_constructor2_test.dart b/tests/language/mixin/forwarding_constructor2_test.dart
index 0c512765037..9afc9131a55 100644
--- a/tests/language/mixin/forwarding_constructor2_test.dart
+++ b/tests/language/mixin/forwarding_constructor2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin1 {
diff --git a/tests/language/mixin/forwarding_constructor3_test.dart b/tests/language/mixin/forwarding_constructor3_test.dart
index 1d2f5dc694e..b3b07d69088 100644
--- a/tests/language/mixin/forwarding_constructor3_test.dart
+++ b/tests/language/mixin/forwarding_constructor3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Verify that a named mixin constructor forwards to the corresponding named
 // base class constructor.
 
diff --git a/tests/language/mixin/forwarding_constructor4_test.dart b/tests/language/mixin/forwarding_constructor4_test.dart
index ece8c133183..29d616be88b 100644
--- a/tests/language/mixin/forwarding_constructor4_test.dart
+++ b/tests/language/mixin/forwarding_constructor4_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Verify that a forwarding constructor is generated even when there is an
 // optional parameter.
 
diff --git a/tests/language/mixin/forwarding_stub_call_test.dart b/tests/language/mixin/forwarding_stub_call_test.dart
index 3cef355ae1c..022dcaa004e 100644
--- a/tests/language/mixin/forwarding_stub_call_test.dart
+++ b/tests/language/mixin/forwarding_stub_call_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test for calling a method for which a forwarding super stub has been
 // inserted.
 
diff --git a/tests/language/mixin/forwarding_stub_set_test.dart b/tests/language/mixin/forwarding_stub_set_test.dart
index e0c2b9ba1ce..26d5603c423 100644
--- a/tests/language/mixin/forwarding_stub_set_test.dart
+++ b/tests/language/mixin/forwarding_stub_set_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test for assigning to a field for which a forwarding super stub has been
 // inserted.
 
diff --git a/tests/language/mixin/forwarding_stub_tearoff_test.dart b/tests/language/mixin/forwarding_stub_tearoff_test.dart
index 470c52e4cfb..c5904093c76 100644
--- a/tests/language/mixin/forwarding_stub_tearoff_test.dart
+++ b/tests/language/mixin/forwarding_stub_tearoff_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test for tearing off a method for which a forwarding super stub has been
 // inserted.
 
diff --git a/tests/language/mixin/generic_test.dart b/tests/language/mixin/generic_test.dart
index eb785f8203a..08701d01c62 100644
--- a/tests/language/mixin/generic_test.dart
+++ b/tests/language/mixin/generic_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S<T> {
diff --git a/tests/language/mixin/getter_regression_test.dart b/tests/language/mixin/getter_regression_test.dart
index 5f9bd22b410..1b271bd5f95 100644
--- a/tests/language/mixin/getter_regression_test.dart
+++ b/tests/language/mixin/getter_regression_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test case for dart2js bug where the getter for y wasn't
 // properly mixed in.
 
diff --git a/tests/language/mixin/illegal_constructor_runtime_test.dart b/tests/language/mixin/illegal_constructor_runtime_test.dart
index 91886bbb643..2e65f967955 100644
--- a/tests/language/mixin/illegal_constructor_runtime_test.dart
+++ b/tests/language/mixin/illegal_constructor_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class M0 {
   factory M0(a, b, c) => throw "uncalled";
   factory M0.named() => throw "uncalled";
diff --git a/tests/language/mixin/illegal_constructor_test.dart b/tests/language/mixin/illegal_constructor_test.dart
index 5b7306dd04d..9ad76fe0a7c 100644
--- a/tests/language/mixin/illegal_constructor_test.dart
+++ b/tests/language/mixin/illegal_constructor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class M0 {
   factory M0(a, b, c) => throw "uncalled";
   factory M0.named() => throw "uncalled";
diff --git a/tests/language/mixin/illegal_cycles_test.dart b/tests/language/mixin/illegal_cycles_test.dart
index 7e47f0104b3..fed0814c2a7 100644
--- a/tests/language/mixin/illegal_cycles_test.dart
+++ b/tests/language/mixin/illegal_cycles_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class M {}
 class M0 extends Object with M0 { }
 //    ^^
diff --git a/tests/language/mixin/illegal_static_access_runtime_test.dart b/tests/language/mixin/illegal_static_access_runtime_test.dart
index edf6b9ac565..c50ce4a2407 100644
--- a/tests/language/mixin/illegal_static_access_runtime_test.dart
+++ b/tests/language/mixin/illegal_static_access_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {
diff --git a/tests/language/mixin/illegal_static_access_test.dart b/tests/language/mixin/illegal_static_access_test.dart
index 6523d32b6ff..e620859a4e9 100644
--- a/tests/language/mixin/illegal_static_access_test.dart
+++ b/tests/language/mixin/illegal_static_access_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {
diff --git a/tests/language/mixin/illegal_super_use_runtime_test.dart b/tests/language/mixin/illegal_super_use_runtime_test.dart
index 86ecb63a1f2..f640879e9c4 100644
--- a/tests/language/mixin/illegal_super_use_runtime_test.dart
+++ b/tests/language/mixin/illegal_super_use_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M {}
diff --git a/tests/language/mixin/illegal_super_use_test.dart b/tests/language/mixin/illegal_super_use_test.dart
index 17e4fad47cd..b53a368da9c 100644
--- a/tests/language/mixin/illegal_super_use_test.dart
+++ b/tests/language/mixin/illegal_super_use_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M {}
diff --git a/tests/language/mixin/illegal_superclass_runtime_test.dart b/tests/language/mixin/illegal_superclass_runtime_test.dart
index 303ca9bde2c..ed4b198e1d7 100644
--- a/tests/language/mixin/illegal_superclass_runtime_test.dart
+++ b/tests/language/mixin/illegal_superclass_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S0 {}
 
 class S1 extends Object {}
diff --git a/tests/language/mixin/illegal_superclass_test.dart b/tests/language/mixin/illegal_superclass_test.dart
index a1b5b8fdad9..56f8f7dfc7d 100644
--- a/tests/language/mixin/illegal_superclass_test.dart
+++ b/tests/language/mixin/illegal_superclass_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S0 {}
 
 class S1 extends Object {}
diff --git a/tests/language/mixin/illegal_syntax_test.dart b/tests/language/mixin/illegal_syntax_test.dart
index 27a695c61e6..2956fa25b83 100644
--- a/tests/language/mixin/illegal_syntax_test.dart
+++ b/tests/language/mixin/illegal_syntax_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S { }
 class G<T> { }
 class M { }
diff --git a/tests/language/mixin/implements2_test.dart b/tests/language/mixin/implements2_test.dart
index 37c0446529d..f4dcc8a5548 100644
--- a/tests/language/mixin/implements2_test.dart
+++ b/tests/language/mixin/implements2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test for named mixin applications with implements clause.
 
 class A {}
diff --git a/tests/language/mixin/implements_test.dart b/tests/language/mixin/implements_test.dart
index 1845773145b..3b546138165 100644
--- a/tests/language/mixin/implements_test.dart
+++ b/tests/language/mixin/implements_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class I0 {
diff --git a/tests/language/mixin/implicit_covariance_test.dart b/tests/language/mixin/implicit_covariance_test.dart
index 87d3ddd6420..2ba51f9ab9b 100644
--- a/tests/language/mixin/implicit_covariance_test.dart
+++ b/tests/language/mixin/implicit_covariance_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 abstract class A<T> {
diff --git a/tests/language/mixin/inference_mixin_field_test.dart b/tests/language/mixin/inference_mixin_field_test.dart
index 96698466c8c..dc22b72aa13 100644
--- a/tests/language/mixin/inference_mixin_field_test.dart
+++ b/tests/language/mixin/inference_mixin_field_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Mixin {
diff --git a/tests/language/mixin/interface_check_test.dart b/tests/language/mixin/interface_check_test.dart
index 9884d1b61cb..bcccdc7b1f5 100644
--- a/tests/language/mixin/interface_check_test.dart
+++ b/tests/language/mixin/interface_check_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class Thing {}
 
 class SubThing extends Thing {
diff --git a/tests/language/mixin/invalid_bound2_test.dart b/tests/language/mixin/invalid_bound2_test.dart
index b53f4dcb57b..99175224a0c 100644
--- a/tests/language/mixin/invalid_bound2_test.dart
+++ b/tests/language/mixin/invalid_bound2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S0<T> {}
 
 class S<U extends num, V extends U> extends S0<String> {}
diff --git a/tests/language/mixin/invalid_bound_test.dart b/tests/language/mixin/invalid_bound_test.dart
index 7f855331955..0ae7e96e664 100644
--- a/tests/language/mixin/invalid_bound_test.dart
+++ b/tests/language/mixin/invalid_bound_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S0<T> {}
 
 class S<T extends num> extends S0<String> {}
diff --git a/tests/language/mixin/invalid_override_in_mixin_runtime_test.dart b/tests/language/mixin/invalid_override_in_mixin_runtime_test.dart
index 7584e4a136e..0f1c994fe9e 100644
--- a/tests/language/mixin/invalid_override_in_mixin_runtime_test.dart
+++ b/tests/language/mixin/invalid_override_in_mixin_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class A {
diff --git a/tests/language/mixin/invalid_override_in_mixin_test.dart b/tests/language/mixin/invalid_override_in_mixin_test.dart
index de7b18cfa8c..75103d92133 100644
--- a/tests/language/mixin/invalid_override_in_mixin_test.dart
+++ b/tests/language/mixin/invalid_override_in_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class A {
diff --git a/tests/language/mixin/is_test.dart b/tests/language/mixin/is_test.dart
index 89b5464aa5e..f62b7165f96 100644
--- a/tests/language/mixin/is_test.dart
+++ b/tests/language/mixin/is_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {}
diff --git a/tests/language/mixin/issue10216_2_test.dart b/tests/language/mixin/issue10216_2_test.dart
index d48fd69fcf9..afb04af44db 100644
--- a/tests/language/mixin/issue10216_2_test.dart
+++ b/tests/language/mixin/issue10216_2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M1 = Object with M0;
diff --git a/tests/language/mixin/issue10216_test.dart b/tests/language/mixin/issue10216_test.dart
index b62c63c8e1e..75950d25459 100644
--- a/tests/language/mixin/issue10216_test.dart
+++ b/tests/language/mixin/issue10216_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class A {
diff --git a/tests/language/mixin/lib_extends_field_test.dart b/tests/language/mixin/lib_extends_field_test.dart
index e509a940cb9..06e63bf2b8d 100644
--- a/tests/language/mixin/lib_extends_field_test.dart
+++ b/tests/language/mixin/lib_extends_field_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library mixin_lib_extends_field_test;
 
 import 'package:expect/expect.dart';
diff --git a/tests/language/mixin/lib_extends_method_test.dart b/tests/language/mixin/lib_extends_method_test.dart
index 59ae2caec27..b022c06f826 100644
--- a/tests/language/mixin/lib_extends_method_test.dart
+++ b/tests/language/mixin/lib_extends_method_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library mixin_lib_extends_method_test;
 
 import "package:expect/expect.dart";
diff --git a/tests/language/mixin/method_override_runtime_test.dart b/tests/language/mixin/method_override_runtime_test.dart
index 6be64db8843..6311d219d78 100644
--- a/tests/language/mixin/method_override_runtime_test.dart
+++ b/tests/language/mixin/method_override_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Signature conformance test.
 abstract class CII {
   int id(int x);
diff --git a/tests/language/mixin/method_override_test.dart b/tests/language/mixin/method_override_test.dart
index e50464d4ac3..31e39ceba73 100644
--- a/tests/language/mixin/method_override_test.dart
+++ b/tests/language/mixin/method_override_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Signature conformance test.
 abstract class CII {
   int id(int x);
diff --git a/tests/language/mixin/method_test.dart b/tests/language/mixin/method_test.dart
index 20ef4648636..1fc61694679 100644
--- a/tests/language/mixin/method_test.dart
+++ b/tests/language/mixin/method_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {
diff --git a/tests/language/mixin/mixin2_test.dart b/tests/language/mixin/mixin2_test.dart
index b9da5794c9b..81110b2f445 100644
--- a/tests/language/mixin/mixin2_test.dart
+++ b/tests/language/mixin/mixin2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M<T> {
diff --git a/tests/language/mixin/mixin3_test.dart b/tests/language/mixin/mixin3_test.dart
index ecdb2bd0d58..097ea8ec82a 100644
--- a/tests/language/mixin/mixin3_test.dart
+++ b/tests/language/mixin/mixin3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M<T> {
diff --git a/tests/language/mixin/mixin4_test.dart b/tests/language/mixin/mixin4_test.dart
index a982532f936..27d5b55baf1 100644
--- a/tests/language/mixin/mixin4_test.dart
+++ b/tests/language/mixin/mixin4_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<T> {}
diff --git a/tests/language/mixin/mixin5_test.dart b/tests/language/mixin/mixin5_test.dart
index 064f53b7374..58dc10dbcb4 100644
--- a/tests/language/mixin/mixin5_test.dart
+++ b/tests/language/mixin/mixin5_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<T> {}
diff --git a/tests/language/mixin/mixin6_test.dart b/tests/language/mixin/mixin6_test.dart
index eb2cadc9b55..a88db2accd9 100644
--- a/tests/language/mixin/mixin6_test.dart
+++ b/tests/language/mixin/mixin6_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<T> {}
diff --git a/tests/language/mixin/mixin7_test.dart b/tests/language/mixin/mixin7_test.dart
index 3c5c28232d8..b2240df8bc6 100644
--- a/tests/language/mixin/mixin7_test.dart
+++ b/tests/language/mixin/mixin7_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<T> {}
diff --git a/tests/language/mixin/mixin_bound2_test.dart b/tests/language/mixin/mixin_bound2_test.dart
index 76da3a9d77f..127c08856f5 100644
--- a/tests/language/mixin/mixin_bound2_test.dart
+++ b/tests/language/mixin/mixin_bound2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<T> {}
diff --git a/tests/language/mixin/mixin_bound_test.dart b/tests/language/mixin/mixin_bound_test.dart
index dfa62738ce3..41dd1c28a94 100644
--- a/tests/language/mixin/mixin_bound_test.dart
+++ b/tests/language/mixin/mixin_bound_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<T> {}
diff --git a/tests/language/mixin/mixin_test.dart b/tests/language/mixin/mixin_test.dart
index 8f32aba8708..ae39319485e 100644
--- a/tests/language/mixin/mixin_test.dart
+++ b/tests/language/mixin/mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M1 {
diff --git a/tests/language/mixin/mixin_type_arguments_test.dart b/tests/language/mixin/mixin_type_arguments_test.dart
index 08a3d9c562f..d179de13925 100644
--- a/tests/language/mixin/mixin_type_arguments_test.dart
+++ b/tests/language/mixin/mixin_type_arguments_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart' show Expect;
 
 @pragma("vm:entry-point") // Prevent obfuscation
diff --git a/tests/language/mixin/named_constructor_test.dart b/tests/language/mixin/named_constructor_test.dart
index 081af92f4f1..ecdd4fee1c5 100644
--- a/tests/language/mixin/named_constructor_test.dart
+++ b/tests/language/mixin/named_constructor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 var calls = <String>[];
diff --git a/tests/language/mixin/naming_test.dart b/tests/language/mixin/naming_test.dart
index a4c267aeeb0..a736fbb9b23 100644
--- a/tests/language/mixin/naming_test.dart
+++ b/tests/language/mixin/naming_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {}
diff --git a/tests/language/mixin/only_for_rti_test.dart b/tests/language/mixin/only_for_rti_test.dart
index d401e85b375..856814061cf 100644
--- a/tests/language/mixin/only_for_rti_test.dart
+++ b/tests/language/mixin/only_for_rti_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Tester<T> {
diff --git a/tests/language/mixin/override_regression_test.dart b/tests/language/mixin/override_regression_test.dart
index cb032e0b4fd..6036a0090b3 100644
--- a/tests/language/mixin/override_regression_test.dart
+++ b/tests/language/mixin/override_regression_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class C0 {
diff --git a/tests/language/mixin/prefix_test.dart b/tests/language/mixin/prefix_test.dart
index 59eb4427904..d40f55ee1fb 100644
--- a/tests/language/mixin/prefix_test.dart
+++ b/tests/language/mixin/prefix_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test for issue 11891.
 
 import "package:expect/expect.dart";
diff --git a/tests/language/mixin/proto_test.dart b/tests/language/mixin/proto_test.dart
index b8b19f184e0..6b57a4fa01e 100644
--- a/tests/language/mixin/proto_test.dart
+++ b/tests/language/mixin/proto_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Tests that a program in csp mode doesn't access the prototype chain
 // on platforms that don't support direct access to __proto__.
 // This test is most useful with --csp and on a platform that doesn't support
diff --git a/tests/language/mixin/recursive_mixin_test.dart b/tests/language/mixin/recursive_mixin_test.dart
index a961ea91a2e..358b60cd886 100644
--- a/tests/language/mixin/recursive_mixin_test.dart
+++ b/tests/language/mixin/recursive_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class A<T> {
diff --git a/tests/language/mixin/regress_11398_test.dart b/tests/language/mixin/regress_11398_test.dart
index eb6079ab164..1b329af27f6 100644
--- a/tests/language/mixin/regress_11398_test.dart
+++ b/tests/language/mixin/regress_11398_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 void main() {
diff --git a/tests/language/mixin/regress_13688_test.dart b/tests/language/mixin/regress_13688_test.dart
index 0c01537298e..e0c44ac614f 100644
--- a/tests/language/mixin/regress_13688_test.dart
+++ b/tests/language/mixin/regress_13688_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class ComparableMixin<E> {
diff --git a/tests/language/mixin/regress_flutter_55345_const_test.dart b/tests/language/mixin/regress_flutter_55345_const_test.dart
index ccf04a946ed..bb4463da8cb 100644
--- a/tests/language/mixin/regress_flutter_55345_const_test.dart
+++ b/tests/language/mixin/regress_flutter_55345_const_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Verifies that references to deduplicated mixins are properly updated
 // in types which are only accessible through constants.
 // Regression test for https://github.com/flutter/flutter/issues/55345.
diff --git a/tests/language/mixin/regress_flutter_55345_test.dart b/tests/language/mixin/regress_flutter_55345_test.dart
index 70df0541174..f7e61db90cc 100644
--- a/tests/language/mixin/regress_flutter_55345_test.dart
+++ b/tests/language/mixin/regress_flutter_55345_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Verifies that references to deduplicated mixins are properly updated.
 // Regression test for https://github.com/flutter/flutter/issues/55345.
 
diff --git a/tests/language/mixin/substitution_test.dart b/tests/language/mixin/substitution_test.dart
index d6121db7129..a422ca6159d 100644
--- a/tests/language/mixin/substitution_test.dart
+++ b/tests/language/mixin/substitution_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that mixins don't interfere with type variable substitution.
 
 import '../dynamic_type_helper.dart';
diff --git a/tests/language/mixin/super_2_test.dart b/tests/language/mixin/super_2_test.dart
index aac47ff41f4..0e0137206dc 100644
--- a/tests/language/mixin/super_2_test.dart
+++ b/tests/language/mixin/super_2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class B {
diff --git a/tests/language/mixin/super_bound_runtime_test.dart b/tests/language/mixin/super_bound_runtime_test.dart
index 62149788666..ad7c91d183c 100644
--- a/tests/language/mixin/super_bound_runtime_test.dart
+++ b/tests/language/mixin/super_bound_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class M<U extends V, V> {}
 
 class N<U, V extends U> {}
diff --git a/tests/language/mixin/super_bound_test.dart b/tests/language/mixin/super_bound_test.dart
index 634c83885ac..a4ffc8ba1cf 100644
--- a/tests/language/mixin/super_bound_test.dart
+++ b/tests/language/mixin/super_bound_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class M<U extends V, V> {}
 
 class N<U, V extends U> {}
diff --git a/tests/language/mixin/super_constructor2_test.dart b/tests/language/mixin/super_constructor2_test.dart
index bb3b60efe6e..4a1c10201f8 100644
--- a/tests/language/mixin/super_constructor2_test.dart
+++ b/tests/language/mixin/super_constructor2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Base {
diff --git a/tests/language/mixin/super_constructor_default_test.dart b/tests/language/mixin/super_constructor_default_test.dart
index 81f2bfc01f1..e248cf9de1d 100644
--- a/tests/language/mixin/super_constructor_default_test.dart
+++ b/tests/language/mixin/super_constructor_default_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Base {
diff --git a/tests/language/mixin/super_constructor_multiple_test.dart b/tests/language/mixin/super_constructor_multiple_test.dart
index 5201be3ddf8..80bd25a6228 100644
--- a/tests/language/mixin/super_constructor_multiple_test.dart
+++ b/tests/language/mixin/super_constructor_multiple_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {
diff --git a/tests/language/mixin/super_constructor_named_test.dart b/tests/language/mixin/super_constructor_named_test.dart
index b16c8156270..433c5c2010f 100644
--- a/tests/language/mixin/super_constructor_named_test.dart
+++ b/tests/language/mixin/super_constructor_named_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Base {
diff --git a/tests/language/mixin/super_constructor_positionals_test.dart b/tests/language/mixin/super_constructor_positionals_test.dart
index d89627649ac..76603b2e547 100644
--- a/tests/language/mixin/super_constructor_positionals_test.dart
+++ b/tests/language/mixin/super_constructor_positionals_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Base {
diff --git a/tests/language/mixin/super_constructor_test.dart b/tests/language/mixin/super_constructor_test.dart
index f342fe88f4d..97e263257aa 100644
--- a/tests/language/mixin/super_constructor_test.dart
+++ b/tests/language/mixin/super_constructor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class Base {
diff --git a/tests/language/mixin/super_use_test.dart b/tests/language/mixin/super_use_test.dart
index f0fc1524545..02a56009df8 100644
--- a/tests/language/mixin/super_use_test.dart
+++ b/tests/language/mixin/super_use_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M {}
diff --git a/tests/language/mixin/superclass_runtime_test.dart b/tests/language/mixin/superclass_runtime_test.dart
index eeb1b9ca1a0..6c986e1aa75 100644
--- a/tests/language/mixin/superclass_runtime_test.dart
+++ b/tests/language/mixin/superclass_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S0 {}
 
 class S1 extends Object {}
diff --git a/tests/language/mixin/superclass_test.dart b/tests/language/mixin/superclass_test.dart
index 5b9a8ee7427..c2ffe52a2ef 100644
--- a/tests/language/mixin/superclass_test.dart
+++ b/tests/language/mixin/superclass_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S0 {}
 
 class S1 extends Object {}
diff --git a/tests/language/mixin/supertype_subclass2_test.dart b/tests/language/mixin/supertype_subclass2_test.dart
index 0bafafc296d..e040e5e0e2d 100644
--- a/tests/language/mixin/supertype_subclass2_test.dart
+++ b/tests/language/mixin/supertype_subclass2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class B {}
 
 class C {}
diff --git a/tests/language/mixin/supertype_subclass_test.dart b/tests/language/mixin/supertype_subclass_test.dart
index 1e2c7cac014..9f3000c7515 100644
--- a/tests/language/mixin/supertype_subclass_test.dart
+++ b/tests/language/mixin/supertype_subclass_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class B {}
 
 class C {}
diff --git a/tests/language/mixin/this_use_test.dart b/tests/language/mixin/this_use_test.dart
index 23d2e994f07..954e49d3dbd 100644
--- a/tests/language/mixin/this_use_test.dart
+++ b/tests/language/mixin/this_use_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that [:this:] in a class A used as a mixin in class D knows it can be an
 // instance of D.
 
diff --git a/tests/language/mixin/type_parameter1_test.dart b/tests/language/mixin/type_parameter1_test.dart
index 1928ec47bb6..4f5f2046b74 100644
--- a/tests/language/mixin/type_parameter1_test.dart
+++ b/tests/language/mixin/type_parameter1_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin1<T> {}
diff --git a/tests/language/mixin/type_parameter2_test.dart b/tests/language/mixin/type_parameter2_test.dart
index 129fdf172f6..a95a516be97 100644
--- a/tests/language/mixin/type_parameter2_test.dart
+++ b/tests/language/mixin/type_parameter2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin1<T> {}
diff --git a/tests/language/mixin/type_parameter3_test.dart b/tests/language/mixin/type_parameter3_test.dart
index 51164d9935b..7d9404a9dd7 100644
--- a/tests/language/mixin/type_parameter3_test.dart
+++ b/tests/language/mixin/type_parameter3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin1<T> {}
diff --git a/tests/language/mixin/type_parameter4_test.dart b/tests/language/mixin/type_parameter4_test.dart
index d309b7f3264..739e5ba8e0f 100644
--- a/tests/language/mixin/type_parameter4_test.dart
+++ b/tests/language/mixin/type_parameter4_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class R<E, F> {}
diff --git a/tests/language/mixin/type_parameter5_test.dart b/tests/language/mixin/type_parameter5_test.dart
index 5f2309cf284..fe667544e52 100644
--- a/tests/language/mixin/type_parameter5_test.dart
+++ b/tests/language/mixin/type_parameter5_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class MixinA<T> {
   T? intField;
 }
diff --git a/tests/language/mixin/type_parameter6_test.dart b/tests/language/mixin/type_parameter6_test.dart
index 8c81ef1d87d..a8ba0297ee8 100644
--- a/tests/language/mixin/type_parameter6_test.dart
+++ b/tests/language/mixin/type_parameter6_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class A<T> {}
 
 class B<S> {
diff --git a/tests/language/mixin/type_parameter_inference_previous_mixin_test.dart b/tests/language/mixin/type_parameter_inference_previous_mixin_test.dart
index a3d9ce53a1d..9edecedb0f9 100644
--- a/tests/language/mixin/type_parameter_inference_previous_mixin_test.dart
+++ b/tests/language/mixin/type_parameter_inference_previous_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class A<T> {
diff --git a/tests/language/mixin/type_parameter_inference_test.dart b/tests/language/mixin/type_parameter_inference_test.dart
index 8d5f336a0af..0f445f703aa 100644
--- a/tests/language/mixin/type_parameter_inference_test.dart
+++ b/tests/language/mixin/type_parameter_inference_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class A<T> {
diff --git a/tests/language/mixin/type_parameters_errors_runtime_test.dart b/tests/language/mixin/type_parameters_errors_runtime_test.dart
index ee3b7ca6abd..524c1e7fd2e 100644
--- a/tests/language/mixin/type_parameters_errors_runtime_test.dart
+++ b/tests/language/mixin/type_parameters_errors_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S<T> {}
 
 class M<U> {}
diff --git a/tests/language/mixin/type_parameters_errors_test.dart b/tests/language/mixin/type_parameters_errors_test.dart
index 25e99b6d77a..21c2409c263 100644
--- a/tests/language/mixin/type_parameters_errors_test.dart
+++ b/tests/language/mixin/type_parameters_errors_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class S<T> {}
 
 class M<U> {}
diff --git a/tests/language/mixin/type_parameters_mixin_extends_test.dart b/tests/language/mixin/type_parameters_mixin_extends_test.dart
index 69f3bbf7b0c..a489793b4f4 100644
--- a/tests/language/mixin/type_parameters_mixin_extends_test.dart
+++ b/tests/language/mixin/type_parameters_mixin_extends_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M<T> {
diff --git a/tests/language/mixin/type_parameters_mixin_test.dart b/tests/language/mixin/type_parameters_mixin_test.dart
index 8a6e569bb36..f55414ba6d3 100644
--- a/tests/language/mixin/type_parameters_mixin_test.dart
+++ b/tests/language/mixin/type_parameters_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class M<T> {
diff --git a/tests/language/mixin/type_parameters_simple_test.dart b/tests/language/mixin/type_parameters_simple_test.dart
index 8721735f73c..51ebec906a2 100644
--- a/tests/language/mixin/type_parameters_simple_test.dart
+++ b/tests/language/mixin/type_parameters_simple_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S {}
diff --git a/tests/language/mixin/type_parameters_super_extends_test.dart b/tests/language/mixin/type_parameters_super_extends_test.dart
index a21e2c3f849..30140c25c47 100644
--- a/tests/language/mixin/type_parameters_super_extends_test.dart
+++ b/tests/language/mixin/type_parameters_super_extends_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S<T> {
diff --git a/tests/language/mixin/type_parameters_super_test.dart b/tests/language/mixin/type_parameters_super_test.dart
index b4c1ee27c29..e89881399d6 100644
--- a/tests/language/mixin/type_parameters_super_test.dart
+++ b/tests/language/mixin/type_parameters_super_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class S<T> {
diff --git a/tests/language/mixin/type_variable_test.dart b/tests/language/mixin/type_variable_test.dart
index 9b4b0df86ed..46623f7c7bb 100644
--- a/tests/language/mixin/type_variable_test.dart
+++ b/tests/language/mixin/type_variable_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test for generic mixin fields.
 
 class A<T> {
diff --git a/tests/language/mixin/typedef_constructor_test.dart b/tests/language/mixin/typedef_constructor_test.dart
index a73fea1116f..b1e13f8f8a7 100644
--- a/tests/language/mixin/typedef_constructor_test.dart
+++ b/tests/language/mixin/typedef_constructor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class A {
diff --git a/tests/language/mixin_constructor_forwarding/const_constructor_test.dart b/tests/language/mixin_constructor_forwarding/const_constructor_test.dart
index ba57bdf6edb..15f42ddb3ba 100644
--- a/tests/language/mixin_constructor_forwarding/const_constructor_test.dart
+++ b/tests/language/mixin_constructor_forwarding/const_constructor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin {
diff --git a/tests/language/mixin_constructor_forwarding/const_constructor_with_field_test.dart b/tests/language/mixin_constructor_forwarding/const_constructor_with_field_test.dart
index e22be63f488..f3dd32c4b79 100644
--- a/tests/language/mixin_constructor_forwarding/const_constructor_with_field_test.dart
+++ b/tests/language/mixin_constructor_forwarding/const_constructor_with_field_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin {
diff --git a/tests/language/mixin_constructor_forwarding/optional_named_parameters_test.dart b/tests/language/mixin_constructor_forwarding/optional_named_parameters_test.dart
index 8cab4c51a84..722fbb1febf 100644
--- a/tests/language/mixin_constructor_forwarding/optional_named_parameters_test.dart
+++ b/tests/language/mixin_constructor_forwarding/optional_named_parameters_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin {
diff --git a/tests/language/mixin_constructor_forwarding/optional_positional_parameters_test.dart b/tests/language/mixin_constructor_forwarding/optional_positional_parameters_test.dart
index 1411223e4cf..96212659252 100644
--- a/tests/language/mixin_constructor_forwarding/optional_positional_parameters_test.dart
+++ b/tests/language/mixin_constructor_forwarding/optional_positional_parameters_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 abstract class Mixin {
diff --git a/tests/language/mixin_declaration/mixin_declaration_factory_test.dart b/tests/language/mixin_declaration/mixin_declaration_factory_test.dart
index fd0e66a6799..332c5d17de8 100644
--- a/tests/language/mixin_declaration/mixin_declaration_factory_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_factory_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // A mixin declaration cannot declare any (factory) constructors.
 
 class A {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B00_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B00_test.dart
index 3a834f0bf8e..02a2c77a839 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B00_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B00_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B01_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B01_test.dart
index b4086d4eb0c..85ad4dba084 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B01_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B01_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B10_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B10_test.dart
index f299b6059a7..275ddda38be 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B10_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B10_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B11_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B11_test.dart
index cc8407603f7..989a2b65dd5 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_B11_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_B11_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C00_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C00_test.dart
index ed966d30328..40ab1fa2b68 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C00_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C00_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C01_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C01_test.dart
index 2157800d532..d48c73485fa 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C01_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C01_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C02_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C02_test.dart
index c1f8c8b74aa..f2977e48785 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C02_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C02_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C10_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C10_test.dart
index c9613ac1cba..d847bd12eff 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C10_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C10_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C11_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C11_test.dart
index 95be3dbed14..4bc07f9eb4b 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C11_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C11_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C12_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C12_test.dart
index 32830724523..5c237be6e49 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_C12_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_C12_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class I<X> {}
diff --git a/tests/language/mixin_declaration/mixin_declaration_inference_valid_mixin_applications_test.dart b/tests/language/mixin_declaration/mixin_declaration_inference_valid_mixin_applications_test.dart
index e65596e4457..c6141420710 100644
--- a/tests/language/mixin_declaration/mixin_declaration_inference_valid_mixin_applications_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_inference_valid_mixin_applications_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 ///////////////////////////////////////////////////////
diff --git a/tests/language/mixin_declaration/mixin_declaration_invalid_override_test.dart b/tests/language/mixin_declaration/mixin_declaration_invalid_override_test.dart
index e84d8af8807..eca336f48fe 100644
--- a/tests/language/mixin_declaration/mixin_declaration_invalid_override_test.dart
+++ b/tests/language/mixin_declaration/mixin_declaration_invalid_override_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 // Test various invalid super-constraints for mixin declarations.
diff --git a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_error_test.dart b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_error_test.dart
index 3566ad66be4..8345c24052a 100644
--- a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_error_test.dart
+++ b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_error_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Requirements=nnbd-weak
 
 // Verifies that a member declared in a null-safe class which overrides
diff --git a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_test.dart b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_test.dart
index 157e0a2c014..1a37895015c 100644
--- a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_test.dart
+++ b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_1_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Requirements=nnbd-weak
 
 // Verify that conflicting implemented interfaces are resolved at a legacy
diff --git a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_2_test.dart b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_2_test.dart
index 01b6d420461..0163e532df1 100644
--- a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_2_test.dart
+++ b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Requirements=nnbd-weak
 
 // Verify that conflicting member signatures are resolved at a legacy
diff --git a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_error_test.dart b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_error_test.dart
index e429b2f8815..543c6f6d4f2 100644
--- a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_error_test.dart
+++ b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_error_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Requirements=nnbd-weak
 
 // Verify that member signatures are computed correctly for null-safe
diff --git a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_test.dart b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_test.dart
index c5ccb58f832..01618f994c5 100644
--- a/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_test.dart
+++ b/tests/language/nnbd/mixed_inheritance/legacy_resolves_conflict_3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Requirements=nnbd-weak
 
 // Verify that member signatures are computed correctly for null-safe
diff --git a/tests/language/optimize/inline_super_field_test.dart b/tests/language/optimize/inline_super_field_test.dart
index b3316f93724..21827e9f314 100644
--- a/tests/language/optimize/inline_super_field_test.dart
+++ b/tests/language/optimize/inline_super_field_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that source maps use the correct compilation unit when super class
 // fields from another compilation unit are inlined.
 
diff --git a/tests/language/private/mixin2_test.dart b/tests/language/private/mixin2_test.dart
index 848f8389195..4bcec755fad 100644
--- a/tests/language/private/mixin2_test.dart
+++ b/tests/language/private/mixin2_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test for testing access to private fields on mixins.
 
 library private_mixin2;
diff --git a/tests/language/private/mixin_exception_throw_test.dart b/tests/language/private/mixin_exception_throw_test.dart
index 96570d7d6c6..5ba1080f94d 100644
--- a/tests/language/private/mixin_exception_throw_test.dart
+++ b/tests/language/private/mixin_exception_throw_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test for http://dartbug.com/11637
 
 class _C {}
diff --git a/tests/language/regress/regress18713_test.dart b/tests/language/regress/regress18713_test.dart
index 01f51d8af60..c1f593ee9f9 100644
--- a/tests/language/regress/regress18713_test.dart
+++ b/tests/language/regress/regress18713_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class T<X> {
diff --git a/tests/language/regress/regress25246_1_test.dart b/tests/language/regress/regress25246_1_test.dart
index 65101deaab8..6f2b9325d5a 100644
--- a/tests/language/regress/regress25246_1_test.dart
+++ b/tests/language/regress/regress25246_1_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'regress25246_2.dart';
 
 class ConcreteClass extends Object with MixIn {}
diff --git a/tests/language/regress/regress26230_test.dart b/tests/language/regress/regress26230_test.dart
index 77792bc4eb5..390a8b8c331 100644
--- a/tests/language/regress/regress26230_test.dart
+++ b/tests/language/regress/regress26230_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class _RenderTabBar extends RenderBox
     with
         ContainerRenderObjectMixin<RenderBox, _TabBarParentData>,
diff --git a/tests/language/regress/regress27957_test.dart b/tests/language/regress/regress27957_test.dart
index 1c5dbcdbf43..75a6147a505 100644
--- a/tests/language/regress/regress27957_test.dart
+++ b/tests/language/regress/regress27957_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 import 'regress27957_lib1.dart' as s1;
 import 'regress27957_lib2.dart' as s2;
diff --git a/tests/language/regress/regress29949_test.dart b/tests/language/regress/regress29949_test.dart
index 8685fae643c..8c28f5b58a2 100644
--- a/tests/language/regress/regress29949_test.dart
+++ b/tests/language/regress/regress29949_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 abstract class S {}
 
 abstract class M<T> {}
diff --git a/tests/language/regress/regress30669_test.dart b/tests/language/regress/regress30669_test.dart
index 967ee54972e..347313f3745 100644
--- a/tests/language/regress/regress30669_test.dart
+++ b/tests/language/regress/regress30669_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class M {
diff --git a/tests/language/regress/regress32267_test.dart b/tests/language/regress/regress32267_test.dart
index 64ed4f31dd2..bca28ba3635 100644
--- a/tests/language/regress/regress32267_test.dart
+++ b/tests/language/regress/regress32267_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // There was a bug in the Kernel mixin transformation: it copied factory
 // constructors from the mixin into the mixin application class.  This could be
 // observed as an unbound type parameter which led to a crash.
diff --git a/tests/language/regress/regress32353_test.dart b/tests/language/regress/regress32353_test.dart
index 080d46d4b88..3cdeacd093a 100644
--- a/tests/language/regress/regress32353_test.dart
+++ b/tests/language/regress/regress32353_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class io_FileSystemEntity {}
diff --git a/tests/language/regress/regress32372_test.dart b/tests/language/regress/regress32372_test.dart
index 2ce2b424a73..dc466234140 100644
--- a/tests/language/regress/regress32372_test.dart
+++ b/tests/language/regress/regress32372_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "package:expect/expect.dart";
 
 class A extends Object with B<String>, C {}
diff --git a/tests/language/regress/regress34235_runtime_test.dart b/tests/language/regress/regress34235_runtime_test.dart
index 9cedc8eed84..71584f54e19 100644
--- a/tests/language/regress/regress34235_runtime_test.dart
+++ b/tests/language/regress/regress34235_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class Base {
   void foo() {}
 }
diff --git a/tests/language/regress/regress34235_test.dart b/tests/language/regress/regress34235_test.dart
index 7451dc5fa4a..89d3da27677 100644
--- a/tests/language/regress/regress34235_test.dart
+++ b/tests/language/regress/regress34235_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 class Base {
   void foo() {}
 }
diff --git a/tests/language/regress/regress34488_runtime_test.dart b/tests/language/regress/regress34488_runtime_test.dart
index 03485de146f..5f44a683f0d 100644
--- a/tests/language/regress/regress34488_runtime_test.dart
+++ b/tests/language/regress/regress34488_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 abstract class Base {
   void f(int i);
   void g([int i]);
diff --git a/tests/language/regress/regress34488_test.dart b/tests/language/regress/regress34488_test.dart
index ff76512033f..2e6e4b6323c 100644
--- a/tests/language/regress/regress34488_test.dart
+++ b/tests/language/regress/regress34488_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 abstract class Base {
   void f(int i);
   void g([int i]);
diff --git a/tests/language/regress/regress34877_test.dart b/tests/language/regress/regress34877_test.dart
index 08ce3d4d2d7..55d8e78b5f7 100644
--- a/tests/language/regress/regress34877_test.dart
+++ b/tests/language/regress/regress34877_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test: ensure that async for loops remain async for loops when
 // mixed in.
 
diff --git a/tests/language/regress/regress65278_test.dart b/tests/language/regress/regress65278_test.dart
index 9edf22c9b3e..d71af419ba3 100644
--- a/tests/language/regress/regress65278_test.dart
+++ b/tests/language/regress/regress65278_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 void main() {
   ContentTabsWidget();
 }
diff --git a/tests/language/regress/regress9602_test.dart b/tests/language/regress/regress9602_test.dart
index 8900388303c..31f393a98e2 100644
--- a/tests/language/regress/regress9602_test.dart
+++ b/tests/language/regress/regress9602_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Regression test case for http://dartbug.com/9602
 library issue9602;
 
diff --git a/tests/language/super/mixin_test.dart b/tests/language/super/mixin_test.dart
index e76a2825fe5..c7a883647b6 100644
--- a/tests/language/super/mixin_test.dart
+++ b/tests/language/super/mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart2js regression test: Test that the type mask for non-null exact Mixin is
 // created for Mixin.getter.
 
diff --git a/tests/language/super/no_such_method4_runtime_test.dart b/tests/language/super/no_such_method4_runtime_test.dart
index f8d48804980..6e3df0bbd3b 100644
--- a/tests/language/super/no_such_method4_runtime_test.dart
+++ b/tests/language/super/no_such_method4_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class A {
diff --git a/tests/language/super/no_such_method4_test.dart b/tests/language/super/no_such_method4_test.dart
index 9e831464f07..62032a73d79 100644
--- a/tests/language/super/no_such_method4_test.dart
+++ b/tests/language/super/no_such_method4_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class A {
diff --git a/tests/language/super/no_such_method5_runtime_test.dart b/tests/language/super/no_such_method5_runtime_test.dart
index 94adb2435cd..497bb5c9037 100644
--- a/tests/language/super/no_such_method5_runtime_test.dart
+++ b/tests/language/super/no_such_method5_runtime_test.dart
@@ -5,6 +5,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class A {
diff --git a/tests/language/super/no_such_method5_test.dart b/tests/language/super/no_such_method5_test.dart
index eb923c13717..ada81d15017 100644
--- a/tests/language/super/no_such_method5_test.dart
+++ b/tests/language/super/no_such_method5_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'package:expect/expect.dart';
 
 class A {
diff --git a/tests/language/superinterface_variance/covariance_test.dart b/tests/language/superinterface_variance/covariance_test.dart
index 11bb1986018..8e718b79996 100644
--- a/tests/language/superinterface_variance/covariance_test.dart
+++ b/tests/language/superinterface_variance/covariance_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 typedef F<X> = X Function();
 typedef G<X> = void Function(void Function(X));
 
diff --git a/tests/language/unsorted/deny_listed_test.dart b/tests/language/unsorted/deny_listed_test.dart
index ba49fdcea8c..785b0ee88f1 100644
--- a/tests/language/unsorted/deny_listed_test.dart
+++ b/tests/language/unsorted/deny_listed_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Dart test checking that static/instance field shadowing do not conflict.
 
 // Test that certain interfaces/classes are denylisted from being
diff --git a/tests/language/vm/regress_32971_test.dart b/tests/language/vm/regress_32971_test.dart
index 6f5863bb1f6..eeff98ee3a0 100644
--- a/tests/language/vm/regress_32971_test.dart
+++ b/tests/language/vm/regress_32971_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test verifying that default switch cast is cloned correctly by the
 // mixin transformation.
 
diff --git a/tests/language/vm/regress_33040_instantiation_test.dart b/tests/language/vm/regress_33040_instantiation_test.dart
index a4970396ebb..20d30809559 100644
--- a/tests/language/vm/regress_33040_instantiation_test.dart
+++ b/tests/language/vm/regress_33040_instantiation_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 //
 // Exact regression test for issue #33040.
 
diff --git a/tests/language/vm/regression_38231_test.dart b/tests/language/vm/regression_38231_test.dart
index a269d67b561..024ec1d58cb 100644
--- a/tests/language/vm/regression_38231_test.dart
+++ b/tests/language/vm/regression_38231_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // VMOptions=--optimization_counter_threshold=1
 
 import "package:expect/expect.dart";
diff --git a/tests/language/void/generalized_void_syntax_test.dart b/tests/language/void/generalized_void_syntax_test.dart
index 02f34044c65..5c9f9aedfa1 100644
--- a/tests/language/void/generalized_void_syntax_test.dart
+++ b/tests/language/void/generalized_void_syntax_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Testing that the reserved word `void` is allowed to occur as a type, not
 // just as a return type.
 
diff --git a/tests/lib/html/html_mock_test.dart b/tests/lib/html/html_mock_test.dart
index 26c2cb11ad8..a8db5c77a93 100644
--- a/tests/lib/html/html_mock_test.dart
+++ b/tests/lib/html/html_mock_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import 'dart:async';
 import 'dart:html';
 
diff --git a/tests/lib/isolate/message3_test.dart b/tests/lib/isolate/message3_test.dart
index a40ece192b7..99b86e07d1a 100644
--- a/tests/lib/isolate/message3_test.dart
+++ b/tests/lib/isolate/message3_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // VMOptions=--no-enable-fast-object-copy
 // VMOptions=--enable-fast-object-copy
 
diff --git a/tests/lib/js/export/static_interop_mock/inheritance_test.dart b/tests/lib/js/export/static_interop_mock/inheritance_test.dart
index b677fc1368a..c712e35ab67 100644
--- a/tests/lib/js/export/static_interop_mock/inheritance_test.dart
+++ b/tests/lib/js/export/static_interop_mock/inheritance_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that @staticInterop extension methods are collected from all extensions,
 // including inheritance.
 
diff --git a/tests/lib/mirrors/abstract_class_test.dart b/tests/lib/mirrors/abstract_class_test.dart
index 17fd28fa7b3..a989c1a41e8 100644
--- a/tests/lib/mirrors/abstract_class_test.dart
+++ b/tests/lib/mirrors/abstract_class_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.abstract_class_test;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/class_declarations_test.dart b/tests/lib/mirrors/class_declarations_test.dart
index 2cbf8dee464..f734cc33fff 100644
--- a/tests/lib/mirrors/class_declarations_test.dart
+++ b/tests/lib/mirrors/class_declarations_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.declarations_test;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/class_mirror_location_other.dart b/tests/lib/mirrors/class_mirror_location_other.dart
index eb94d21d6ce..3b72aa13dac 100644
--- a/tests/lib/mirrors/class_mirror_location_other.dart
+++ b/tests/lib/mirrors/class_mirror_location_other.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 part of test.class_location;
 
 class ClassInOtherFile {}
diff --git a/tests/lib/mirrors/class_mirror_location_test.dart b/tests/lib/mirrors/class_mirror_location_test.dart
index 0af1f59a5b4..1c54bcb73e8 100644
--- a/tests/lib/mirrors/class_mirror_location_test.dart
+++ b/tests/lib/mirrors/class_mirror_location_test.dart
@@ -1,6 +1,11 @@
 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // 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.
+
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.class_location;
 
 import "dart:mirrors";
diff --git a/tests/lib/mirrors/fake_function_without_call_test.dart b/tests/lib/mirrors/fake_function_without_call_test.dart
index 3d80c03b0cf..6ec6aae4ba4 100644
--- a/tests/lib/mirrors/fake_function_without_call_test.dart
+++ b/tests/lib/mirrors/fake_function_without_call_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 import "dart:mirrors";
 
 import "package:expect/expect.dart";
diff --git a/tests/lib/mirrors/generic_interface_test.dart b/tests/lib/mirrors/generic_interface_test.dart
index 061685d7660..7cc2ef3b245 100644
--- a/tests/lib/mirrors/generic_interface_test.dart
+++ b/tests/lib/mirrors/generic_interface_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.generic_bounded;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/generic_mixin_applications_test.dart b/tests/lib/mirrors/generic_mixin_applications_test.dart
index 0880347214a..e685ee991d7 100644
--- a/tests/lib/mirrors/generic_mixin_applications_test.dart
+++ b/tests/lib/mirrors/generic_mixin_applications_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.generic_mixin_applications;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/generic_mixin_test.dart b/tests/lib/mirrors/generic_mixin_test.dart
index c52c756e96f..a2c0c5f376d 100644
--- a/tests/lib/mirrors/generic_mixin_test.dart
+++ b/tests/lib/mirrors/generic_mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.generic_mixin;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/instance_members_easier_test.dart b/tests/lib/mirrors/instance_members_easier_test.dart
index ccd1b4ffa05..65c2edd79b3 100644
--- a/tests/lib/mirrors/instance_members_easier_test.dart
+++ b/tests/lib/mirrors/instance_members_easier_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.instance_members;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/instance_members_test.dart b/tests/lib/mirrors/instance_members_test.dart
index 1eeb39a7e36..bdfd4a38607 100644
--- a/tests/lib/mirrors/instance_members_test.dart
+++ b/tests/lib/mirrors/instance_members_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.instance_members;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/library_declarations_test.dart b/tests/lib/mirrors/library_declarations_test.dart
index 80cd982c8ed..d174bb4102f 100644
--- a/tests/lib/mirrors/library_declarations_test.dart
+++ b/tests/lib/mirrors/library_declarations_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.library_declarations_test;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/mixin_application_test.dart b/tests/lib/mirrors/mixin_application_test.dart
index ccefda22d18..46394aa780a 100644
--- a/tests/lib/mirrors/mixin_application_test.dart
+++ b/tests/lib/mirrors/mixin_application_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // This test uses the multi-test "ok" feature to create two positive tests from
 // one file. One of these tests fail on dart2js, but pass on the VM, or vice
 // versa.
diff --git a/tests/lib/mirrors/mixin_members_test.dart b/tests/lib/mirrors/mixin_members_test.dart
index 57202f1aca1..fc54707ff78 100644
--- a/tests/lib/mirrors/mixin_members_test.dart
+++ b/tests/lib/mirrors/mixin_members_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library mixin_members_test;
 
 import "dart:mirrors";
diff --git a/tests/lib/mirrors/mixin_simple_test.dart b/tests/lib/mirrors/mixin_simple_test.dart
index ee1c97461cd..8de58cacc7c 100644
--- a/tests/lib/mirrors/mixin_simple_test.dart
+++ b/tests/lib/mirrors/mixin_simple_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.mixin;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/mixin_test.dart b/tests/lib/mirrors/mixin_test.dart
index de9f3308ba8..33d990a4386 100644
--- a/tests/lib/mirrors/mixin_test.dart
+++ b/tests/lib/mirrors/mixin_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.mixin;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/parameter_of_mixin_app_constructor_test.dart b/tests/lib/mirrors/parameter_of_mixin_app_constructor_test.dart
index c2baee9c7a1..1ea5dfda699 100644
--- a/tests/lib/mirrors/parameter_of_mixin_app_constructor_test.dart
+++ b/tests/lib/mirrors/parameter_of_mixin_app_constructor_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.parameter_of_mixin_app_constructor;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/reflected_type_generics_test.dart b/tests/lib/mirrors/reflected_type_generics_test.dart
index 0e581b783e7..f4fa445b545 100644
--- a/tests/lib/mirrors/reflected_type_generics_test.dart
+++ b/tests/lib/mirrors/reflected_type_generics_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.reflected_type_generics_test;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/repeated_private_anon_mixin_app_test.dart b/tests/lib/mirrors/repeated_private_anon_mixin_app_test.dart
index 04f50b9b82f..3b0acd1c992 100644
--- a/tests/lib/mirrors/repeated_private_anon_mixin_app_test.dart
+++ b/tests/lib/mirrors/repeated_private_anon_mixin_app_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.repeated_private_anon_mixin_app;
 
 // Regression test for symbol mangling.
diff --git a/tests/lib/mirrors/static_members_test.dart b/tests/lib/mirrors/static_members_test.dart
index 74cbb4202c3..b5d9ce35139 100644
--- a/tests/lib/mirrors/static_members_test.dart
+++ b/tests/lib/mirrors/static_members_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 library test.static_members;
 
 import 'dart:mirrors';
diff --git a/tests/lib/mirrors/typedef_metadata_test.dart b/tests/lib/mirrors/typedef_metadata_test.dart
index 7b5e09872d5..0a6b8dafdb0 100644
--- a/tests/lib/mirrors/typedef_metadata_test.dart
+++ b/tests/lib/mirrors/typedef_metadata_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 @string
 @symbol
 library test.typedef_metadata_test;
diff --git a/tests/lib/mirrors/unnamed_mixin_application_test.dart b/tests/lib/mirrors/unnamed_mixin_application_test.dart
index d8844955715..2520029834e 100644
--- a/tests/lib/mirrors/unnamed_mixin_application_test.dart
+++ b/tests/lib/mirrors/unnamed_mixin_application_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 /// Test that the forwarding constructors of unnamed mixin applications are
 /// included for reflection.
 
diff --git a/tests/lib_2/js/export/static_interop_mock/inheritance_test.dart b/tests/lib_2/js/export/static_interop_mock/inheritance_test.dart
index 048f14828b2..201a5dc1037 100644
--- a/tests/lib_2/js/export/static_interop_mock/inheritance_test.dart
+++ b/tests/lib_2/js/export/static_interop_mock/inheritance_test.dart
@@ -4,6 +4,10 @@
 //
 // @dart=2.19
 
+// TODO(51557): Decide if the mixins being applied in this test should be
+// "mixin", "mixin class" or the test should be left at 2.19.
+// @dart=2.19
+
 // Test that @staticInterop extension methods are collected from all extensions,
 // including inheritance.