anchor.diff:      ));
       handler = server.handlerFor('web');
   
  -    nextBuild = new Completer<Null>();
  -    subscription = server.buildResults.listen((_) {
  -      if (!nextBuild.isCompleted) {
  -        nextBuild.complete();
  -        nextBuild = new Completer<Null>();
  -      }
  +    nextBuild = new Completer<BuildResult>();
  +    subscription = server.buildResults.listen((result) {
  +      nextBuild.complete(result);
  +      nextBuild = new Completer<BuildResult>();
       });
       await nextBuild.future;
     });
  
positive.code:     FakeWatcher.notifyWatchers(
        new WatchEvent(ChangeType.ADD, '$path/web/new.txt'),
      );
      await nextBuild.future;
      final response = await handler(new Request('GET', getNew));
      expect(await response.readAsString(), 'NEW');
    }, skip: 'Enable on fix of https://github.com/dart-lang/build/issues/500');
  }
  
  class UppercaseBuilder implements Builder {
  
negative.code:   InMemoryRunnerAssetReader reader;
    InMemoryRunnerAssetWriter writer;
    StreamSubscription subscription;
    Completer<BuildResult> nextBuild;
  
    final path = p.absolute('example');
  
  