Enzymeでwindow.alertのunit testを実装してみる

window.alertにjest.fn()を代入してtestを進めることで実現可能

it('trigger window.alert on click button', () => {
  window.alert = jest.fn()
  const wrapper = shallow(<Button onClick={window.alert('hogehoge')} />)
  wrapper.simulate('click')
  expect(window.alert.mock.calls.length).toBe(1)
  expect(window.alert).toHaveBeenCalledWith('hogehoge')
})

参考

Unit testing your React application with Jest and Enzyme