Update tests of sealed mixin on type to reflect spec change.

As of https://github.com/dart-lang/language/pull/2889 it is an error
to declare a mixin with an `on` type which is declared in a different
library.

Change-Id: I02d6b3b6c203a46c74d2eacd006181db8e563726
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/290022
Reviewed-by: Kallen Tu <kallentu@google.com>

tests/language/sealed_class/sealed_class_mixin_on_error_test.dart

@@ -0,0 +1,35 @@
+// Copyright (c) 2023, 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
+
+import 'sealed_class_mixin_on_lib.dart';
+
+// It is an error to declare a mixin with an `on` type which is a sealed class
+// from another library.
+mixin MA on SealedClass {}
+//          ^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+// It is not an error to declare a mixin with an `on` type which is a subtype of
+// a sealed class from another library if the subclass is not otherwise
+// restricted.
+mixin MB on A {}
+
+// It is an error to apply a mixin with an `on` type which is sealed to the
+// sealed class which is its `on` type outside of the library which declares the
+// `on` type.
+class ConcreteA extends SealedClass with M {}
+//                      ^^^^^^^^^^^
+// [analyzer] COMPILE_TIME_ERROR.INVALID_USE_OF_TYPE_OUTSIDE_LIBRARY
+// [cfe] The class 'SealedClass' can't be extended, implemented, or mixed in outside of its library because it's a sealed class.
+
+// It is not an error to apply a mixin with an `on` type which is sealed to a
+// subtype of the sealed class.
+class ConcreteB extends A with M {}
+
+// It is not an error to apply a mixin with an `on` type which is a subtype of a
+// sealed class from another library to a subtype of the sealed class.
+class ConcreteC extends A with MB {}

tests/language/sealed_class/sealed_class_mixin_on_lib.dart

@@ -1,4 +1,4 @@
-// Copyright (c) 2022, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2023, 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.
 
@@ -12,8 +12,8 @@ abstract class A extends SealedClass {}
 
 class B extends SealedClass {}
 
-sealed mixin SealedMixin {}
+// It is legal to declare a mixin whose `on` type is a sealed type from the
+// same library.
+mixin M on SealedClass {}
 
-class C extends SealedClass with SealedMixin {}
-
-class D with SealedMixin {}
+class C extends SealedClass with M {}

tests/language/sealed_class/sealed_class_mixin_on_test.dart

@@ -1,41 +0,0 @@
-// 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 a sealed type to appear in the "on" clause of a mixin declaration in
-// another library.
-
-import "package:expect/expect.dart";
-import 'sealed_class_mixin_on_lib.dart';
-
-mixin MA on SealedClass {}
-mixin MB on SealedClass {}
-
-class ConcreteA extends A with MA, MB {
-  int foo = 0;
-}
-
-mixin MC on SealedClass, SealedMixin {}
-
-class ConcreteC extends C with MC {
-  int foo = 0;
-}
-
-mixin MCSingular on SealedMixin {}
-
-class ConcreteD extends D with MCSingular {
-  int foo = 0;
-}
-
-main() {
-  var concreteA = ConcreteA();
-  Expect.equals(0, concreteA.foo);
-
-  var concreteC = ConcreteC();
-  Expect.equals(0, concreteC.foo);
-
-  var concreteD = ConcreteD();
-  Expect.equals(0, concreteD.foo);
-}