diff --git a/tests/language/sealed_class/sealed_class_as_mixin_in_lib_error_test.dart b/tests/language/sealed_class/sealed_class_as_mixin_in_lib_test.dart
similarity index 52%
rename from tests/language/sealed_class/sealed_class_as_mixin_in_lib_error_test.dart
rename to tests/language/sealed_class/sealed_class_as_mixin_in_lib_test.dart
index 12dec23c4a8..156a091033d 100644
--- a/tests/language/sealed_class/sealed_class_as_mixin_in_lib_error_test.dart
+++ b/tests/language/sealed_class/sealed_class_as_mixin_in_lib_test.dart
@@ -4,7 +4,7 @@
 
 // SharedOptions=--enable-experiment=sealed-class
 
-// Error when attempting to mix in a sealed class inside of library.
+// Allow mixing in a sealed class inside of library.
 
 sealed class SealedClass {
   int nonAbstractFoo = 0;
@@ -17,14 +17,8 @@ class Class {}
 mixin Mixin {}
 
 abstract class A with SealedClass {}
-//             ^
-// [analyzer] unspecified
-// [cfe] Class 'SealedClass' can't be used as a mixin.
 
 class B with SealedClass {
-//    ^
-// [analyzer] unspecified
-// [cfe] Class 'SealedClass' can't be used as a mixin.
   @override
   int nonAbstractFoo = 100;
 
@@ -36,27 +30,11 @@ class B with SealedClass {
 }
 
 abstract class C = Object with SealedClass;
-//             ^
-// [analyzer] unspecified
-// [cfe] Class 'SealedClass' can't be used as a mixin.
 
 abstract class D with SealedClass, Class {}
-//             ^
-// [analyzer] unspecified
-// [cfe] Class 'Class' can't be used as a mixin.
-// [cfe] Class 'SealedClass' can't be used as a mixin.
 
 class E with Class, SealedMixin {}
-//    ^
-// [analyzer] unspecified
-// [cfe] Class 'Class' can't be used as a mixin.
 
 abstract class F with Mixin, SealedClass {}
-//             ^
-// [analyzer] unspecified
-// [cfe] Class 'SealedClass' can't be used as a mixin.
 
 class G with Mixin, Class {}
-//    ^
-// [analyzer] unspecified
-// [cfe] Class 'Class' can't be used as a mixin.
diff --git a/tests/language/sealed_class/sealed_class_as_mixin_old_version_lib.dart b/tests/language/sealed_class/sealed_class_as_mixin_old_version_lib.dart
new file mode 100644
index 00000000000..327bdca9485
--- /dev/null
+++ b/tests/language/sealed_class/sealed_class_as_mixin_old_version_lib.dart
@@ -0,0 +1,9 @@
+// Copyright (c) 2022, 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.
+
+// @dart = 2.18
+
+class Class {}
+
+mixin Mixin {}
diff --git a/tests/language/sealed_class/sealed_class_as_mixin_old_version_test.dart b/tests/language/sealed_class/sealed_class_as_mixin_old_version_test.dart
new file mode 100644
index 00000000000..c67dc6af76f
--- /dev/null
+++ b/tests/language/sealed_class/sealed_class_as_mixin_old_version_test.dart
@@ -0,0 +1,27 @@
+// Copyright (c) 2022, 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.
+
+// SharedOptions=--enable-experiment=sealed-class
+
+// Allow mixing in a sealed class outside of library when the version of the
+// library of the class being mixed-in is older than the version that
+// `sealed-class` is being shipped in.
+
+import 'sealed_class_as_mixin_old_version_lib.dart';
+
+abstract class OutsideA with Class {}
+
+class OutsideB with Class {}
+
+class OutsideC = Object with Class;
+
+abstract class OutsideD with Class, Mixin {}
+
+class OutsideE with Class, Mixin {}
+
+sealed class OutsideF with Class {}
+
+sealed class OutsideG with Class, Mixin {}
+
+sealed class OutsideH = Object with Class;
diff --git a/tests/language/sealed_class/sealed_class_implement_error_test.dart b/tests/language/sealed_class/sealed_class_implement_error_test.dart
index c8fda06a358..8ce0a955ef5 100644
--- a/tests/language/sealed_class/sealed_class_implement_error_test.dart
+++ b/tests/language/sealed_class/sealed_class_implement_error_test.dart
@@ -15,7 +15,7 @@ abstract class OutsideA implements SealedClass {}
 // [cfe] Sealed class 'SealedClass' can't be extended, implemented, or mixed in outside of its library.
 
 class OutsideB implements SealedClass {
-// [error column 1, length 344]
+// [error column 1, length 423]
 // [analyzer] COMPILE_TIME_ERROR.SEALED_CLASS_SUBTYPE_OUTSIDE_OF_LIBRARY
 //    ^
 // [cfe] Sealed class 'SealedClass' can't be extended, implemented, or mixed in outside of its library.
diff --git a/tests/language/sealed_class/sealed_class_typedef_error_test.dart b/tests/language/sealed_class/sealed_class_typedef_error_test.dart
index 8535f9fb51c..58c0a9a1875 100644
--- a/tests/language/sealed_class/sealed_class_typedef_error_test.dart
+++ b/tests/language/sealed_class/sealed_class_typedef_error_test.dart
@@ -16,7 +16,7 @@ class ATypeDef extends SealedClassTypeDef {}
 // [cfe] Sealed class 'SealedClass' can't be extended, implemented, or mixed in outside of its library.
 
 class BTypeDef implements SealedClassTypeDef {
-// [error column 1, length 213]
+// [error column 1, length 292]
 // [analyzer] COMPILE_TIME_ERROR.SEALED_CLASS_SUBTYPE_OUTSIDE_OF_LIBRARY
 //    ^
 // [cfe] Sealed class 'SealedClass' can't be extended, implemented, or mixed in outside of its library.
diff --git a/tests/language/sealed_class/sealed_class_typedef_used_outside_error_test.dart b/tests/language/sealed_class/sealed_class_typedef_used_outside_error_test.dart
index 7bb6707552e..4c49f63b3de 100644
--- a/tests/language/sealed_class/sealed_class_typedef_used_outside_error_test.dart
+++ b/tests/language/sealed_class/sealed_class_typedef_used_outside_error_test.dart
@@ -19,7 +19,7 @@ class A extends ATypeDef {}
 // [cfe] Sealed class 'SealedClass' can't be extended, implemented, or mixed in outside of its library.
 
 class B implements ATypeDef {
-// [error column 1, length 184]
+// [error column 1, length 263]
 // [analyzer] COMPILE_TIME_ERROR.SEALED_CLASS_SUBTYPE_OUTSIDE_OF_LIBRARY
 //    ^
 // [cfe] Sealed class 'SealedClass' can't be extended, implemented, or mixed in outside of its library.
diff --git a/tests/language/sealed_class/sealed_mixin_with_error_test.dart b/tests/language/sealed_class/sealed_mixin_with_error_test.dart
index 329aa930350..5a61176935d 100644
--- a/tests/language/sealed_class/sealed_mixin_with_error_test.dart
+++ b/tests/language/sealed_class/sealed_mixin_with_error_test.dart
@@ -15,7 +15,7 @@ abstract class OutsideA with SealedMixin {}
 // [cfe] Sealed mixin 'SealedMixin' can't be mixed in outside of its library.
 
 class OutsideB with SealedMixin {
-// [error column 1, length 218]
+// [error column 1, length 297]
 // [analyzer] COMPILE_TIME_ERROR.SEALED_MIXIN_SUBTYPE_OUTSIDE_OF_LIBRARY
 //    ^
 // [cfe] Sealed mixin 'SealedMixin' can't be mixed in outside of its library.