Split unittest tests into separate test files.

pkg/unittest/test/unittest_excess_callback_test.dart

+// Copyright (c) 2013, 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 unittestTest;
+import 'dart:isolate';
+import 'dart:async';
+import 'package:unittest/unittest.dart';
+
+part 'unittest_test_utils.dart';
+
+var testName = 'excess callback test';
+
+var testFunction = (TestConfiguration testConfig) {
+  test(testName, () {
+    var _callback0 = expectAsync0(() => ++testConfig.count);
+    var _callback1 = expectAsync0(() => ++testConfig.count);
+    var _callback2 = expectAsync0(() {
+      _callback1();
+      _callback1();
+      _callback0();
+    });
+    _defer(_callback2);
+  });
+};
+
+var expected = buildStatusString(0, 1, 0, testName,
+    count: 1, message: 'Callback called more times than expected (1).');