*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.
expect(stubStyle.fontFamily).toEqual('Arial');
      expect(stubStyle.lineHeight).toEqual('1.2');
      styles.fontFamily = 'Helvetica';
      ReactDOM.render(<div style={styles} />, container);
      expect(stubStyle.display).toEqual('none');
      expect(stubStyle.fontFamily).toEqual('Arial');
      expect(stubStyle.lineHeight).toEqual('1.2');
      styles.lineHeight = 0.5;
      ReactDOM.render(<div style={styles} />, container);
      expect(stubStyle.display).toEqual('none');
      expect(stubStyle.fontFamily).toEqual('Arial');
      expect(stubStyle.lineHeight).toEqual('1.2');
      ReactDOM.render(<div style={undefined} />, container);
      expect(stubStyle.display).toBe('');
      expect(stubStyle.fontFamily).toBe('');
      expect(stubStyle.lineHeight).toBe('');
    });
    it('should throw when mutating style objects', () => {
      var style = {border: '1px solid black'};
      class App extends React.Component {
        state = {style: style};
        render() {
          return <div style={this.state.style}>asd</div>;
        }
      }
      ReactTestUtils.renderIntoDocument(<App />);
      expectDev(() => (style.position = 'absolute')).toThrow();
    });
    it('should warn for unknown prop', () => {
      spyOn(console, 'error');