Improved error messages from unittest.

pkg/unittest/lib/src/iterable_matchers.dart

Index: pkg/unittest/lib/src/iterable_matchers.dart
===================================================================
--- pkg/unittest/lib/src/iterable_matchers.dart	(revision 23884)
+++ pkg/unittest/lib/src/iterable_matchers.dart	(working copy)
@@ -42,7 +42,7 @@
     if (matchState.state != null) {
       var index = matchState.state['index'];
       var element = matchState.state['element'];
-      mismatchDescription.add('position $index ');
+      mismatchDescription.add('at position $index ');
       return _matcher.describeMismatch(element, mismatchDescription,
             matchState.state['state'], verbose);
     }
@@ -95,7 +95,7 @@
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     if (item is !Iterable) {
-      return mismatchDescription.add('not an Iterable');
+      return mismatchDescription.add('is not an Iterable');
     } else {
       return _matcher.describeMismatch(item, mismatchDescription,
           matchState, verbose);
@@ -230,14 +230,15 @@
   Description describeMismatch(item, Description mismatchDescription,
                                MatchState matchState, bool verbose) {
     if (item is !Iterable) {
-      return mismatchDescription.add('not an Iterable');
+      return mismatchDescription.add('is not an Iterable');
     } else if (item.length != _expected.length) {
       return mismatchDescription.
-          add('length was ${item.length} instead of ${_expected.length}');
+          add('has length ${item.length} instead of ${_expected.length}');
     } else {
       return mismatchDescription.
+          add('has ').
           addDescriptionOf(matchState.state["actual"]).
-          add(' not $_description ').
+          add(' which is not $_description ').
           addDescriptionOf(matchState.state["expected"]).
           add(' at position ${matchState.state["index"]}');
     }