We should be able to look at see if the child has a data-react-id attribute but isn't rendered by this copy of React and consequently warn.

See https://groups.google.com/forum/#!topic/reactjs/mdwfKKJ0L2Q.

/**
 * Copyright 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @emails react-core
 */
'use strict';
var React;
var ReactDOM;
var ReactDOMServer;
var ReactMount;
var ReactTestUtils;
var WebComponents;
describe('ReactMount', function() {
  beforeEach(function() {
    jest.resetModuleRegistry();
    React = require('React');
    ReactDOM = require('ReactDOM');
    ReactDOMServer = require('ReactDOMServer');
    ReactMount = require('ReactMount');
    ReactTestUtils = require('ReactTestUtils');
    try {