sample of shadow rendering and triggering a state change

App.test.js

import React from 'react';
import { shallow } from 'enzyme';
import App from './App';

it('button changes color of box', () => {
  const app = shallow(<App />);
  expect(app.find('.box').length).toEqual(1);
  app.find('button').last().simulate('click');
  expect(app.find('.box.red').length).toEqual(1);
});