Extracted from https://github.com/facebook/react/issues/12643.

We're currently diff a host node in the complete phase even if it has bailed out in the begin phase. By itself, this just means we're doing a little bit more work than necessary. But it also has some observable effects. In particular, https://github.com/facebook/react/issues/13424 (which by itself would be very rare and probably not worth fixing) is made worse because we end up committing update to inputs from another component.

I have a fix for this in https://github.com/facebook/react/pull/13423. Filing this for posterity.
simulateMouseMove(null, firstTarget);
      expect(ops).toEqual(['enter parent']);
      ops = [];
      simulateMouseMove(firstTarget, secondTarget);
      expect(ops).toEqual([
        
        'enter portal',
      ]);
      ops = [];
      simulateMouseMove(secondTarget, thirdTarget);
      expect(ops).toEqual([
        'leave portal',
        'leave parent', 
      ]);
    } finally {
      document.body.removeChild(container);
      document.body.removeChild(portalContainer);
    }
  });
  it('should throw on bad createPortal argument', () => {
    expect(() => {
      ReactDOM.createPortal(<div>portal</div>, null);
    }).toThrow('Target container is not a DOM element.');
    expect(() => {
      ReactDOM.createPortal(<div>portal</div>, document.createTextNode('hi'));
    }).toThrow('Target container is not a DOM element.');
  });
  it('should warn for non-functional event listeners', () => {
    class Example extends React.Component {
      render() {