我是React和测试的新手，所以请原谅这个问题的天真。我有一个React表单组件，它在输入上运行一个函数handleChange。尝试用Jest测试它，但无法使其工作。
下面是Login组件：

class Login extends React.Component {

  constructor() {
    super();
    this.state = {username: '', password: ''}
    this.disableSubmit = this.disableSubmit.bind(this);
    this.handleChange = this.handleChange.bind(this);
  }

  handleChange(e) {
    this.setState({
      [e.target.name]: e.target.value
    });
  }

  render() {

    return(
      <div className="login">
        <form>
          <h3 className="login__title">LOGIN</h3>
          <div className="input-group">
            <input onChange={this.handleChange} value={this.state.username} className="form-control login__input username" type="text" placeholder="user name" name={'username'} autoFocus/>
          </div>
          <div className="input-group">
            <input onChange={this.handleChange} value={this.state.password} className="form-control login__input password" type="password" placeholder="password" name={'password'}/>
          </div>
          <div>
            <button className="btn btn-primary btn-block login__button" type="submit">Login</button>
          </div>
        </form>
      </div>

    )
  }
}

export default Login;

字符串
这是我的测试：

import React from 'react'
import { shallow, mount } from 'enzyme'
import { shallowToJson } from 'enzyme-to-json'

import {Login} from '../../../src/base/components/index'

describe('Given the Login component is rendered', () => {

  describe('Snapshots', () => {
    let component

    beforeEach(() => {
      component = shallow(<Login />)
    })

    it('should be as expected', () => {
      expect(shallowToJson(component)).toMatchSnapshot()
    })
  })

})

test('Submitting the form should call handleSubmit', () => {

  const startState = {username: ''};
  const handleChange = jest.fn();
  const login = mount(<Login />);
  const userInput = login.find('.username');

  userInput.simulate('change');

  expect(handleChange).toBeCalled();

})

型
快照测试通过良好，但在最后一次尝试中，我的函数测试失败：

TypeError: Cannot read property 'target' of undefined

型
我想我需要传递一些东西给函数。有点困惑！
先谢谢你的帮助。
更新：
按如下所述更改测试，但测试失败：expect(jest.fn()).toBeCalled() Expected mock function to have been called.个
测试更新：

test('Input should call handleChange on change event', () => {

  const login = mount(<Login />);
  const handleChange = jest.spyOn(login.instance(), 'handleChange');
  const userInput = login.find('.username');
  const event = {target: {name: "username", value: "usertest"}};

  userInput.simulate('change', event);

  expect(handleChange).toBeCalled();

})

型