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.
state = {flip: false, count: 0};
        flip() {
          this.setState({flip: true, count: this.state.count + 1});
        }
        tick() {
          this.setState({count: this.state.count + 1});
        }
        render() {
          const useB = !this.props.forceA && this.state.flip;
          return <div onClick={useB ? handlerB : handlerA} />;
        }
      }
      class Click extends React.Component {
        constructor() {
          super();
          click(node);
        }
        render() {
          return null;
        }
      }
      let inst;
      ReactDOM.render([<Example key="a" ref={n => (inst = n)} />], container);
      const node = container.firstChild;
      expect(node.tagName).toEqual('DIV');
      function click(target) {