sert_equals(e.currentSrc, '');
      t.step_timeout(function() {
        if (src == '') {
          assert_equals(e.currentSrc, '');
        } else {
          assert_equals(e.currentSrc, e.src);
        }
        t.done();
      }, 0);
    }, tagName + '.currentSrc after setting src attribute "' + src + '"');

    async_test(function(t) {
      var e = document.createElement(tagName);
      var s = document.createElement('source');
      s.src = src;
      e.appendChild(s);
      assert_equals(e.currentSrc