Add an Invoker class that manages a running test.

test/utils.dart

Index: test/utils.dart
diff --git a/test/utils.dart b/test/utils.dart
new file mode 100644
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--- /dev/null
+++ b/test/utils.dart
@@ -0,0 +1,28 @@
+// Copyright (c) 2015, 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.
+
+library unittest.test.utils;
+
+import 'dart:async';
+
+import 'package:unittest/unittest.dart';
+
+/// Returns a matcher that matches a [TestFailure] with the given [message].
+Matcher isTestFailure(String message) => predicate(
+    (error) => error is TestFailure && error.message == message,
+    'is a TestFailure with message "$message"');
+
+/// Returns a [Future] that completes after pumping the event queue [times]
+/// times.
+///
+/// By default, this should pump the event queue enough times to allow any code
+/// to run, as long as it's not waiting on some external event.
+Future pumpEventQueue([int times=20]) {
+  if (times == 0) return new Future.value();
+  // Use [new Future] future to allow microtask events to finish. The [new
+  // Future.value] constructor uses scheduleMicrotask itself and would therefore
+  // not wait for microtask callbacks that are scheduled after invoking this
+  // method.
+  return new Future(() => pumpEventQueue(times - 1));
+}