Added async_helper and fixed broken asynchronous test.

tests/lib/async/run_async6_test.dart

Index: tests/lib/async/run_async6_test.dart
diff --git a/tests/lib/async/run_async6_test.dart b/tests/lib/async/run_async6_test.dart
index e89bc038568eeef213a44eba8f5b71ba1aa17420..1cd08f9f7deee4b8501f0048f809e78440872910 100644
--- a/tests/lib/async/run_async6_test.dart
+++ b/tests/lib/async/run_async6_test.dart
@@ -11,12 +11,9 @@ bool _unhandledExceptionCallback(exception) => true;
 
 main() {
   test('run async test', () {
-    var callback = expectAsync0(() {});
-    runAsync(() {
-      runAsync(() {
-        callback();
-      });
+    runAsync(expectAsync0({
+      runAsync(expectAsync0(() {}));

[floitsch, 2013/06/20 14:59:35]

why is this change needed?

[kustermann, 2013/06/25 07:14:21]

You're right, this should not be necessary.

       throw new Exception('exception');
-    });
+    }));
   });
 }