anchor.diff:        });
   
         test('attributes', () {
  +        // TODO(ussuri): Add similar tests for statically declared attributes
  +        // (e.g. <spark-button primary large noPadding></>).
           final btnElt = (dom.document.querySelector('#default') as SparkButton);
           expect(btnElt, isNotNull);
           final btn = btnElt.getShadowDomElement('#button');
  
positive.code:         expect(btn.classes.contains('btn-primary'), isFalse);
          expect(btn.classes.contains('btn-default'), isTrue);
          expect(btn.classes.contains('active'), isFalse);
          expect(btn.classes.contains('disabled'), isTrue);
          expect(btn.classes.contains('btn-lg'), isFalse);
          expect(btn.classes.contains('btn-sm'), isTrue);
  
negative.code:         expect(btn.classes.contains('btn-primary'), isTrue);
          expect(btn.classes.contains('btn-default'), isFalse);
          expect(btn.classes.contains('active'), isTrue);
          expect(btn.classes.contains('enabled'), isTrue);
          expect(btn.classes.contains('disabled'), isFalse);
          expect(btn.classes.contains('btn-lg'), isTrue);
          expect(btn.classes.contains('btn-sm'), isFalse);
  