Jest and mocking

jest_test.js

import React from 'react';
import ReactDOM from 'react-dom';
import { mount } from 'enzyme'
import ReactTestUtils from 'react-addons-test-utils'
import * as api from './api';

it('renders without crashing', () => {
  api.sayHello = jest.fn()
  api.sayHello.mockImplementation( (x) => "boom" )

  let App = require('./App').default
  const dom = mount(<App/>)
  dom.ref("name").node.value="mark"
  dom.find("button").simulate( 'click' )
  expect(api.sayHello).toBeCalledWith("mark")
});