*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.
render() {
          return <div style={{margin: '0'}} />;
        }
      }
      ReactTestUtils.renderIntoDocument(<Component />);
      expectDev(console.error.calls.count()).toBe(0);
    });
    it('should warn nicely about NaN in style', () => {
      spyOn(console, 'error');
      var style = {fontSize: NaN};
      var div = document.createElement('div');
      ReactDOM.render(<span style={style} />, div);
      ReactDOM.render(<span style={style} />, div);
      expectDev(console.error.calls.count()).toBe(1);
      expectDev(console.error.calls.argsFor(0)[0]).toEqual(
        'Warning: `NaN` is an invalid value for the `fontSize` css style property.',
      );
    });
    it('should update styles if initially null', () => {
      var styles = null;
      var container = document.createElement('div');
      ReactDOM.render(<div style={styles} />, container);