         assert.closeTo(rect.left - (window.innerWidth - rect.right), 0, 5, 'centered horizontally');
          assert.closeTo(rect.top - (window.innerHeight - rect.bottom), 0, 5, 'centered vertically');
        });

        test('scrolling element is constrained to viewport height', function() {
          var el = fixture('sized-x');
          makeScrolling(el);
          el.refit();
          var rect = el.getBoundingClientRect();
          assert.isTrue(rect.height <= window.innerHeight, 'height is less 