Use package:testing for tools/gardening

tools/gardening/test/parse_build_results_test.dart

 // Copyright (c) 2017, 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.
 
 import 'package:args/args.dart';
 import 'package:expect/expect.dart';
 import 'package:gardening/src/buildbot_structures.dart';
 import 'package:gardening/src/util.dart';
 
 import 'test_client.dart';
 
-// TODO(johnniwinther): Use 'package:testing' to run all tests.
 main(List<String> args) async {
   ArgParser argParser = createArgParser();
   argParser.addFlag('force', abbr: 'f');
   ArgResults argResults = argParser.parse(args);
   processArgResults(argResults);
 
   TestClient client = new TestClient(force: argResults['force']);
   BuildUri buildUri =
       new BuildUri.fromUrl('https://build.chromium.org/p/client.dart/builders/'
           'vm-kernel-linux-debug-x64-be/builds/1884/steps/'
@@ skipping 10 matching lines @@
     }
     Expect.isNotNull(status, "TestStatus for '$testName' not found.");
     Expect.equals(
         expectedStatus, status.status, "Unexpected status for '$testName'.");
   }
 
   checkTest('corelib/list_growable_test', 'pass');
   checkTest('corelib_2/map_keys2_test', 'fail');
   client.close();
 }