*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.argsFor(1)[0]).toContain('onKeyDown');
    });
    it('should warn about class', () => {
      spyOn(console, 'error');
      ReactTestUtils.renderIntoDocument(
        React.createElement('div', {class: 'muffins'}),
      );
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toContain('className');
    });
    it('should warn about class (ssr)', () => {
      spyOn(console, 'error');
      ReactDOMServer.renderToString(
        React.createElement('div', {class: 'muffins'}),
      );
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toContain('className');
    });
    it('should warn about props that are no longer supported', () => {
      spyOn(console, 'error');
      ReactTestUtils.renderIntoDocument(<div />);
      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 without case sensitivity', () => {
      spyOn(console, 'error');
      ReactTestUtils.renderIntoDocument(<div />);