anchor.diff:      });
   
       describe("when provider returns empty list of assets", () {
  -      beforeEach(() => buildTransformer(htmlWithCss, []));
  +      beforeEach(() => buildTransformer(htmlWithCss));
   
  -      it("no outputs are added to transform", () {
  +      it("doesn't add any outputs", () {
           transformer.apply(transform).then(expectAsync((_) {
             transform.getLogs(callsTo("addOutput")).verify(neverHappened);
           }));
  
positive.code:     Mock primaryInput;
      SpriteAssetProviderMock provider;
  
      void buildTransformer(String html, List<Asset> assets, [SpriteSheet spriteSheet]) {
        primaryInput.when(callsTo("readAsString")).alwaysReturn(new Future.value(html));
        var spriteSheetEngine = new TestSpriteSheetEngine()
            ..when(callsTo("generate")).alwaysReturn(new Future.value(spriteSheet));
  
negative.code:     });
  
      describe("when primary input has linked stylesheets", () {
        beforeEach(() => buildTransformer(htmlWithCss));
  
        it("requests provider for assets", () {
          transformer.apply(transform).then(expectAsync((_) => provider
  