Add a testOn parameter to test() and group().

test/utils.dart

Index: test/utils.dart
diff --git a/test/utils.dart b/test/utils.dart
index 0bdeee1297cb1c246b43d053bec1f4320be309b5..22573c8a6b25b1f635bcf064cc3cb37a2fc8e8b2 100644
--- a/test/utils.dart
+++ b/test/utils.dart
@@ -9,6 +9,7 @@ import 'dart:collection';
 
 import 'package:unittest/src/backend/invoker.dart';
 import 'package:unittest/src/backend/live_test.dart';
+import 'package:unittest/src/backend/metadata.dart';
 import 'package:unittest/src/backend/state.dart';
 import 'package:unittest/src/backend/suite.dart';
 import 'package:unittest/src/runner/load_exception.dart';
@@ -178,7 +179,7 @@ Future pumpEventQueue([int times=20]) {
 
 /// Returns a local [LiveTest] that runs [body].
 LiveTest createTest(body()) {
-  var test = new LocalTest("test", body);
+  var test = new LocalTest("test", new Metadata(), body);
   var suite = new Suite([test]);
   return test.load(suite);
 }