Create an apptesting framework for dart.

third_party/dart-packages/matcher/matcher/src/prints_matcher.dart

 // 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.
 
 library matcher.prints_matcher;
 
 import 'dart:async';
 
 import 'description.dart';
 import 'expect.dart';
@@ skipping 53 matching lines @@
         .describeMismatch(actual, new StringDescription(), matchState, verbose)
         .toString();
 
     if (innerMismatch.isNotEmpty) {
       description.add('\n   Which: ').add(innerMismatch.toString());
     }
 
     return description;
   }
 }