pkg/matcher: upgrate tests to test

test/test_utils.dart

 // 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.
 
 library matcher.test_utils;
 
 import 'dart:collection';
 
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 void shouldFail(value, Matcher matcher, expected) {
   var failed = false;
   try {
     expect(value, matcher);
   } on TestFailure catch (err) {
     failed = true;
 
     var _errorString = err.message;
 
@@ skipping 57 matching lines @@
       _current = _count;
       _count--;
       return true;
     }
     _current = null;
     return false;
   }
 
   int get current => _current;
 }