|  | // Copyright (c) 2024, 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. | 
|  |  | 
|  | import 'package:expect/expect.dart'; | 
|  |  | 
|  | mixin Foo { | 
|  | String foo({String? a = 'default'}) => 'Foo.$a'; | 
|  | } | 
|  |  | 
|  | class A extends Object with Foo { | 
|  | String foo({String? a}) => 'a.foo(a: $a)'; | 
|  | } | 
|  |  | 
|  | class B extends Object with Foo { | 
|  | String foo({String? a}) => super.foo(a: a); | 
|  | } | 
|  |  | 
|  | void main() { | 
|  | final a = A(); | 
|  | final b = B(); | 
|  | Expect.equals('a.foo(a: null)', a.foo(a: null)); | 
|  | Expect.equals('Foo.', b.foo(a: '')); | 
|  | Expect.equals('Foo.null', b.foo()); | 
|  | } |