*feature*

>Warning: A component is `contentEditable` and contains `children` managed by React. It is now your responsibility to guarantee that none of those nodes are unexpectedly modified or duplicated. This is probably not intentional.

It would help heaps if I would know _which_ component is causing this.
expectDev(console.error.calls.count()).toBe(0);
      ReactTestUtils.renderIntoDocument(<div onfocusin={() => {}} />);
      expectDev(console.error.calls.count()).toBe(1);
      ReactTestUtils.renderIntoDocument(<div onfocusout={() => {}} />);
      expectDev(console.error.calls.count()).toBe(2);
    });
    it('should warn about props that are no longer supported (ssr)', () => {
      spyOn(console, 'error');
      ReactDOMServer.renderToString(<div />);
      expectDev(console.error.calls.count()).toBe(0);
      ReactDOMServer.renderToString(<div onFocusIn={() => {}} />);
      expectDev(console.error.calls.count()).toBe(1);
      ReactDOMServer.renderToString(<div onFocusOut={() => {}} />);
      expectDev(console.error.calls.count()).toBe(2);
    });
    it('should warn about props that are no longer supported without case sensitivity (ssr)', () => {
      spyOn(console, 'error');
      ReactDOMServer.renderToString(<div />);
      expectDev(console.error.calls.count()).toBe(0);
      ReactDOMServer.renderToString(<div onfocusin={() => {}} />);
      expectDev(console.error.calls.count()).toBe(1);
      ReactDOMServer.renderToString(<div onfocusout={() => {}} />);
      expectDev(console.error.calls.count()).toBe(2);
    });
    it('gives source code refs for unknown prop warning', () => {
      spyOn(console, 'error');
      ReactTestUtils.renderIntoDocument(<div class="paladin" />);
      ReactTestUtils.renderIntoDocument(<input type="text" onclick="1" />);
      expectDev(console.error.calls.count()).toBe(2);
      expectDev(normalizeCodeLocInfo(console.error.calls.argsFor(0)[0])).toBe(