Currently if React is not loaded, ReactDOM shows this:

<img width="664" alt="screen shot 2017-08-08 at 3 36 52 pm" src="https://user-images.githubusercontent.com/810438/29077217-784c7624-7c4f-11e7-88bc-b055407523a9.png">

We should throw a nicer error message in the entry point I think.
render() {
        return <div>Foo</div>;
      }
    }
    const element = <Foo />;
    
    let called = false;
    ReactDOM.render(element, container, () => (called = true));
    expect(called).toEqual(true);
    
    called = false;
    ReactDOM.unstable_batchedUpdates(() => {
      ReactDOM.render(element, container, () => (called = true));
    });
    expect(called).toEqual(true);
  });
  if (ReactDOMFeatureFlags.useFiber) {
    it('should render a component returning strings directly from render', () => {
      const Text = ({value}) => value;
      ReactDOM.render(<Text value="foo" />, container);
      expect(container.textContent).toEqual('foo');
    });
    it('should render a component returning numbers directly from render', () => {
      const Text = ({value}) => value;
      ReactDOM.render(<Text value={10} />, container);
      expect(container.textContent).toEqual('10');
    });
    it('finds the DOM Text node of a string child', () => {
      class Text extends React.Component {