Added ability to disable logging in mocks, to avoid the memory overhead if you don't need behavior …

lib/unittest/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.
 
 /**
  * This is the main assertion function. It asserts that [actual]
  * matches the [matcher]. [matcher] is optional and defaults to isTrue,
  * so expect can be used with a single predicate argument. [reason]
  * is optional and is typically not supplied if a reasonable matcher is
  * explicitly provided, as a reason can be generated from the matcher.
@@ skipping 94 matching lines @@
 
 // The error message formatter for failed asserts.
 ErrorFormatter _assertErrorFormatter = null;
 
 // The default error formatter implementation.
 String _defaultErrorFormatter(actual, Matcher matcher, String reason) {
   var description = new StringDescription();
   description.add('Expected: ').addDescriptionOf(matcher).
       add('\n     but: ');
   matcher.describeMismatch(actual, description);
+  description.add('.\n');
   if (reason != null) {
-    description.add('\n').add(reason).add('\n');
+    description.add(reason).add('\n');
   }
   return description.toString();
 }
 
 /**
  * Changes or resets to default the failure message formatter for expect().
  * [formatter] is a reference to the new formatter; if this is omitted or
  * null then the failure formatter is reset to the default. The new
  * formatter is returned; this allows custom expect handlers to easily
  * get a reference to the default formatter.
  */
 ErrorFormatter configureExpectFormatter([ErrorFormatter formatter = null]) {
   if (formatter == null) {
     formatter = _defaultErrorFormatter;
   }
   return _assertErrorFormatter = formatter;
 }