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.

expect(console.error.calls.argsFor(0)[0]).toContain(
      ' (client) nbsp entity: &nbsp; client text</div>\n' +
      ' (server) nbsp entity: &nbsp; server text</div>'
    );
  });
  if (WebComponents !== undefined) {
    it('should allow mounting/unmounting to document fragment container', function() {
      var shadowRoot;
      var proto = Object.create(HTMLElement.prototype, {
        createdCallback: {
          value: function() {
            shadowRoot = this.createShadowRoot();
            ReactDOM.render(<div>Hi, from within a WC!</div>, shadowRoot);
            expect(shadowRoot.firstChild.tagName).toBe('DIV');
            ReactDOM.render(<span>Hi, from within a WC!</span>, shadowRoot);
            expect(shadowRoot.firstChild.tagName).toBe('SPAN');
          },
        },
      });
      proto.unmount = function() {
        ReactDOM.unmountComponentAtNode(shadowRoot);
      };
      document.registerElement('x-foo', {prototype: proto});
      var element = document.createElement('x-foo');
      element.unmount();
    });
  }
  it('should warn if render removes React-rendered children', function() {
    var container = document.createElement('container');
    class Component extends React.Component {