add string-equals to unittest, fix implementation in expect.dart

client/testing/unittest/shared.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Description text of the current test group. If multiple groups are nested,
  * this will contain all of their text concatenated.
  */
 String _currentGroup = '';
 
@@ skipping 245 matching lines @@
  * Wraps an value and provides an "==" operator that can be used to verify that
  * the value matches a given expectation.
  */
 class Expectation {
   final _value;
 
   Expectation(this._value);
 
   /** Asserts that the value is equivalent to [expected]. */
   void equals(expected) {
-    Expect.equals(expected, _value);
+    if (_value is String && expected is String) {
+      Expect.stringEquals(expected, _value);
+    } else {
+      Expect.equals(expected, _value);
+    }
   }
 
   /**
    * Asserts that the difference between [expected] and the value is within
    * [tolerance]. If no tolerance is given, it is assumed to be the value 4
    * significant digits smaller than the expected value.
    */
   void approxEquals(num expected,
       [num tolerance = null, String reason = null]) {
     Expect.approxEquals(expected, _value, tolerance: tolerance, reason: reason);
@@ skipping 77 matching lines @@
   }
 
   void error(String message_, String stackTrace_) {
     result = _ERROR;
     this.message = message_;
     this.stackTrace = stackTrace_;
   }
 }
 
 typedef void TestFunction();