item-b');
      });
      test('mixins are re-evaluated with element upgrade', function() {
        function checkBg(node) {
          var itemA = node.querySelector('x-item-a');
          var itemB = node.querySelector('x-item-b');
          var itemA_BG = getComputedStyle(itemA)['background-color'].trim();
          var itemB_BG = getComputedStyle(itemB)['background-color'].trim();
          assert.equal(itemA_BG, itemB_BG, 'x-item-a and x-item-b should have the same background color');
        }
        