The error event on `<source>` elements doesn't work. Looking at #4370, it seems like there is an `onError` for `<video>` but I can't tell if that's supposed to work for `<source>` too.

The error event is useful so I can deduce which format the browser is using.

var re = '^' + quoteRegexp(expected) + '$';
              return {
                pass: (new RegExp(re)).test(actual),
              };
            },
          };
        },
      });
    });
    it('should handle dangerouslySetInnerHTML', function() {
      var innerHTML = {__html: 'testContent'};
      expect(
        genMarkup({dangerouslySetInnerHTML: innerHTML})
      ).toHaveInnerhtml('testContent');
    });
  });
  describe('mountComponent', function() {
    var mountComponent;
    beforeEach(function() {
      mountComponent = function(props) {
        var container = document.createElement('div');
        ReactDOM.render(<div {...props} />, container);
      };
    });
    it('should not duplicate uppercased selfclosing tags', function() {
      var Container = React.createClass({
        render: function() {
          return React.createElement('BR', null);
        },
      });