Remove package:unittest from some tests

tests/language/async_star_test.dart

 // 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 async_star_test;
 
-import "package:unittest/unittest.dart";
+import "package:test/test.dart";
 import "dart:async";
 
 main() {
   group("basic", () {
     test("empty", () {
       f() async* {}
       return f().toList().then((v) {
         expect(v, equals([]));
       });
     });
@@ skipping 758 matching lines @@
 var getErrors = new StreamTransformer.fromHandlers(
   handleData:(data, sink) { fail("Unexpected value"); },
   handleError: (e, s, sink) { sink.add(e); },
   handleDone: (sink) { sink.close(); });
 
 class NotAStream {
   listen(oData, {onError, onDone, cancelOnError}) {
     fail("Not implementing Stream.");
   }
 }