Big merge from experimental to bleeding edge.

sdk/lib/core/expect.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.
 
 part of dart.core;
 
 /**
  * Expect is used for tests that do not want to make use of the
  * Dart unit test library - for example, the core language tests.
  * Third parties are discouraged from using this, and should use
@@ skipping 102 matching lines @@
       if (expected[i] != actual[i]) {
         _fail('Expect.listEquals(at index $i, '
               'expected: <${expected[i]}>, actual: <${actual[i]}>$msg) fails');
       }
     }
     // We check on length at the end in order to provide better error
     // messages when an unexpected item is inserted in a list.
     if (expected.length != actual.length) {
       _fail('Expect.listEquals(list length, '
         'expected: <${expected.length}>, actual: <${actual.length}>$msg) '
-        'fails');
+        'fails: Next element <'
+        '${expected.length > n ? expected[n] : actual[n]}>');
     }
   }
 
   /**
    * Checks that all [expected] and [actual] have the same set of keys (using
    * the semantics of [Map.containsKey] to determine what "same" means. For
    * each key, checks that the values in both maps are equal using `==`.
    */
   static void mapEquals(Map expected, Map actual, [String reason = null]) {
     String msg = _getMessage(reason);
@@ skipping 155 matching lines @@
 
 bool _identical(a, b) => identical(a, b);
 
 typedef bool _CheckExceptionFn(exception);
 
 class ExpectException implements Exception {
   ExpectException(this.message);
   String toString() => message;
   String message;
 }