Add pretty-printing to unittest and more thoroughly print values.

pkg/unittest/lib/src/iterable_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 which matches [Iterable]s in which all elements
  * match the given [matcher].
  */
@@ skipping 24 matching lines @@
   }
 
   Description describe(Description description) =>
       description.add('every element ').addDescriptionOf(_matcher);
 
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     if (matchState.state != null) {
       var index = matchState.state['index'];
       var element = matchState.state['element'];
+      mismatchDescription.add('position $index ');
       return _matcher.describeMismatch(element, mismatchDescription,
-            matchState.state['state'], verbose).add(' at position $index');
+            matchState.state['state'], verbose);
     }
     return super.describeMismatch(item, mismatchDescription,
           matchState, verbose);
   }
 }
 
 /**
  * Returns a matcher which matches [Iterable]s in which at least one
  * element matches the given [matcher].
  */
@@ skipping 179 matching lines @@
     } else {
       return mismatchDescription.
           addDescriptionOf(matchState.state["actual"]).
           add(' not $_description ').
           addDescriptionOf(matchState.state["expected"]).
           add(' at position ${matchState.state["index"]}');
     }
   }
 }