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.

if (WebComponents === undefined && typeof jest !== 'undefined') {
        WebComponents = require('WebComponents');
      }
    } catch (e) {
      
      
      
    }
  });
  describe('unmountComponentAtNode', function() {
    it('throws when given a non-node', function() {
      var nodeArray = document.getElementsByTagName('div');
      expect(function() {
        ReactDOM.unmountComponentAtNode(nodeArray);
      }).toThrowError(
        'unmountComponentAtNode(...): Target container is not a DOM element.'
      );
    });
  });
  it('throws when given a string', function() {
    expect(function() {
      ReactTestUtils.renderIntoDocument('div');
    }).toThrowError(
      'ReactDOM.render(): Invalid component element. Instead of passing a ' +
      'string like \'div\', pass React.createElement(\'div\') or <div />.'
    );
  });
  it('throws when given a factory', function() {
    class Component extends React.Component {
      render() {