Add an option to run skipped tests.

test/utils.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.
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:test/src/backend/declarer.dart';
 import 'package:test/src/backend/group.dart';
 import 'package:test/src/backend/group_entry.dart';
@@ skipping 287 matching lines @@
   expect(success, isTrue);
 }
 
 /// Runs [body] with a declarer and returns the declared entries.
 List<GroupEntry> declare(void body()) {
   var declarer = new Declarer()..declare(body);
   return declarer.build().entries;
 }
 
 /// Runs [body] with a declarer and returns an engine that runs those tests.
-Engine declareEngine(void body()) {
+Engine declareEngine(void body(), {bool runSkipped: false}) {
   var declarer = new Declarer()..declare(body);
   return new Engine.withSuites([
     new RunnerSuite(const PluginEnvironment(), declarer.build())
-  ]);
+  ], runSkipped: runSkipped);
 }