Revert "Remove package:unittest from some tests"

tests/lib/async/schedule_microtask2_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 run_async_test;
 
+import 'package:expect/expect.dart';
 import 'dart:async';
-import 'package:test/test.dart';
+import 'package:unittest/unittest.dart';
 
 main() {
   // Check that the callbacks are executed in order.
   test("run async in order test", () {
     int lastCallback = -1;
     for (int i = 0; i < 100; i++) {
       scheduleMicrotask(expectAsync(() {
-        expect(lastCallback, equals(i - 1));
+        Expect.equals(lastCallback, i - 1);
         lastCallback = i;
       }));
     }
   });
 }