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.
'<div>portal2[0]:a</div><div>portal2[1]:a</div>',
      );
      expect(container.innerHTML).toBe(
        '<div>normal[0]:a</div><div>normal[1]:a</div>',
      );
      expect(ops).toEqual([
        'normal[0]:a componentDidMount',
        'portal1[0]:a componentDidMount',
        'normal[1]:a componentDidMount',
        'portal2[0]:a componentDidMount',
        'portal2[1]:a componentDidMount',
        'Parent:a componentDidMount',
      ]);
      ops.length = 0;
      ReactDOM.render(<Parent step="b" />, container);
      expect(portalContainer1.innerHTML).toBe('<div>portal1[0]:b</div>');
      expect(portalContainer2.innerHTML).toBe(
        '<div>portal2[0]:b</div><div>portal2[1]:b</div>',
      );
      expect(container.innerHTML).toBe(
        '<div>normal[0]:b</div><div>normal[1]:b</div>',
      );
      expect(ops).toEqual([
        'normal[0]:b componentDidUpdate',
        'portal1[0]:b componentDidUpdate',
        'normal[1]:b componentDidUpdate',
        'portal2[0]:b componentDidUpdate',
        'portal2[1]:b componentDidUpdate',
        'Parent:b componentDidUpdate',
      ]);