Currently, if you define `shouldComponentUpdate` on `React.PureComponent` nothing bad happens and it acts like `React.Component` https://jsfiddle.net/jekmdfva/

We should probably warn in dev since it defaults the point of `PureComponent`
return <div>{this.props.text[0]}</div>;
      }
    }
    var container = document.createElement('div');
    var text;
    var component;
    text = ['porcini'];
    component = ReactDOM.render(<Component text={text} />, container);
    expect(container.textContent).toBe('porcini');
    expect(renders).toBe(1);
    text = ['morel'];
    component = ReactDOM.render(<Component text={text} />, container);
    expect(container.textContent).toBe('morel');
    expect(renders).toBe(2);
    text[0] = 'portobello';
    component = ReactDOM.render(<Component text={text} />, container);
    expect(container.textContent).toBe('morel');
    expect(renders).toBe(2);
    
    component.setState({type: 'mushrooms'});
    expect(container.textContent).toBe('morel');
    expect(renders).toBe(2);
    
    component.setState({type: 'portobello mushrooms'});
    expect(container.textContent).toBe('portobello');
    expect(renders).toBe(3);
  });
  it('can override shouldComponentUpdate', () => {
    var renders = 0;
    class Component extends React.PureComponent {