Clean up isolate tests.

tests/isolate/simple_message_test.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.
 
 // Dart test program for testing that isolates are spawned.
 
 library IsolateNegativeTest;
 import "package:expect/expect.dart";
 import 'dart:isolate';
-import '../../pkg/unittest/lib/unittest.dart';
+import "package:async_helper/async_helper.dart";
 
 void entry(SendPort replyTo) {
-  replyTo.send("foo");
+  var message = "foo";
+  message = "bar";  /// 01: runtime error
+  replyTo.send(message);
 }
 
 main() {
-  test("ensure isolate code is executed", () {
-    ReceivePort response = new ReceivePort();
-    Isolate.spawn(entry, response.sendPort);
-    response.first.then(expectAsync1((message) {
-      expect("Expected fail", isTrue);   // <=-------- Should fail here.
-    }));
+  asyncStart();
+  ReceivePort response = new ReceivePort();
+  Isolate.spawn(entry, response.sendPort);
+  response.first.then((message) {
+    Expect.equals("foo", message);
+    asyncEnd();
   });
 }