a === b -> identical(a, b)

pkg/unittest/lib/src/core_matchers.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 matcher;
 
 /**
  * Returns a matcher that matches empty strings, maps or collections.
  */
 const Matcher isEmpty = const _Empty();
@@ skipping 55 matching lines @@
 
 /**
  * Returns a matches that matches if the value is the same instance
  * as [object] (`===`).
  */
 Matcher same(expected) => new _IsSameAs(expected);
 
 class _IsSameAs extends BaseMatcher {
   final _expected;
   const _IsSameAs(this._expected);
-  bool matches(item, MatchState matchState) => item === _expected;
+  bool matches(item, MatchState matchState) => identical(item, _expected);
   // If all types were hashable we could show a hash here.
   Description describe(Description description) =>
       description.add('same instance as ').addDescriptionOf(_expected);
 }
 
 /**
  * Returns a matcher that does a deep recursive match. This only works
  * with scalars, Maps and Iterables. To handle cyclic structures a
  * recursion depth [limit] can be provided. The default limit is 100.
  */
@@ skipping 624 matching lines @@
       description.add(_featureDescription).add(' ').addDescriptionOf(_matcher);
 
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     mismatchDescription.add(_featureName).add(' ');
     _matcher.describeMismatch(matchState.state['feature'], mismatchDescription,
         matchState.state['innerState'], verbose);
     return mismatchDescription;
   }
 }