Use package:testing for tools/gardening

tools/gardening/bin/summary.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 'dart:async';
 import 'package:args/args.dart';
 import 'package:gardening/src/bot.dart';
 import 'package:gardening/src/buildbot_data.dart';
 import 'package:gardening/src/buildbot_structures.dart';
 import 'package:gardening/src/util.dart';
 
 void help(ArgParser argParser) {
   print('Summarizes the current status of the build bot.');
   print('Usage: summary [options] (<group> ...)');
   print("  where <group> is (part of) a build bot group, like 'vm-kernel', ");
   print("  and options are:");
   print(argParser.usage);
 }
 
-main(List<String> args) async {
+Future main(List<String> args) async {
   ArgParser argParser = createArgParser();
   ArgResults argResults = argParser.parse(args);
   processArgResults(argResults);
   if (argResults['help']) {
     help(argParser);
     return;
   }
 
   Bot bot = new Bot(logdog: argResults['logdog']);
   List<BuildResult> buildResultsWithoutFailures = <BuildResult>[];
@@ skipping 52 matching lines @@
       print(' Found ${buildResultsWithFailures.length} '
           'test steps with failures:');
       for (BuildResult result in buildResultsWithFailures) {
         print('  ${result.buildUri.toUri()}');
       }
     }
   }
 
   bot.close();
 }