Some unit test fixes:

lib/unittest/core_matchers.dart

Index: lib/unittest/core_matchers.dart
===================================================================
--- lib/unittest/core_matchers.dart	(revision 8626)
+++ lib/unittest/core_matchers.dart	(working copy)
@@ -141,8 +141,6 @@
  * The value passed to expect() should be a reference to the function.
  * Note that the function cannot take arguments; to handle this
  * a wrapper will have to be created.
- * The function will be called once upon success, or twice upon failure
- * (the second time to get the failure description).
  */
 Matcher throwsA(Matcher matcher) => new _Throws(matcher);
 
@@ -179,11 +177,11 @@
   }
 
   Description describeMismatch(item, Description mismatchDescription) {
-    try {
-      item();
+    if (_matcher == null) {
       return mismatchDescription.add(' no exception');
-    } catch (final e) {
-      return mismatchDescription.add(' exception does not match ').
+    } else {
+      return mismatchDescription.
+          add(' no exception or exception does not match ').
           addDescriptionOf(_matcher);
     }
   }