https://jsfiddle.net/3apqnhmw/

```jsx
class Foo extends React.Component {
  render() {
     return <div>Foo</div>
  }
}

class App extends React.Component {
  render() {
    return Foo
  }
}
```

When `App` returns `Foo` instead of `<Foo />` accidentally, Fiber does not catch this.
render() {
        var inner = (
          <Wrapper object={innerObj} ref={c => (this.innerRef = c)} />
        );
        var outer = (
          <Wrapper object={outerObj} ref={c => (this.outerRef = c)}>
            {inner}
          </Wrapper>
        );
        return outer;
      }
      componentDidMount() {
        expect(this.innerRef.getObject()).toEqual(innerObj);
        expect(this.outerRef.getObject()).toEqual(outerObj);
        mounted = true;
      }
    }
    ReactTestUtils.renderIntoDocument(<Component />);
    expect(mounted).toBe(true);
  });
  it('should support new-style refs with mixed-up owners', () => {
    class Wrapper extends React.Component {