We should be able to look at see if the child has a data-react-id attribute but isn't rendered by this copy of React and consequently warn.

See https://groups.google.com/forum/#!topic/reactjs/mdwfKKJ0L2Q.

return <div />;
      }
    }
    expect(function() {
      ReactTestUtils.renderIntoDocument(Component);
    }).toThrowError(
      'ReactDOM.render(): Invalid component element. Instead of passing a ' +
      'class like Foo, pass React.createElement(Foo) or <Foo />.'
    );
  });
  it('should render different components in same root', function() {
    var container = document.createElement('container');
    document.body.appendChild(container);
    ReactMount.render(<div></div>, container);
    expect(container.firstChild.nodeName).toBe('DIV');
    ReactMount.render(<span></span>, container);
    expect(container.firstChild.nodeName).toBe('SPAN');
  });
  it('should unmount and remount if the key changes', function() {
    var container = document.createElement('container');
    var mockMount = jest.fn();
    var mockUnmount = jest.fn();
    var Component = React.createClass({
      componentDidMount: mockMount,
      componentWillUnmount: mockUnmount,
      render: function() {
        return <span>{this.props.text}</span>;
      },
    });
    expect(mockMount.mock.calls.length).toBe(0);