用 jest 和酶窥探 React 功能组件方法；无法窥探原始值

Question

我正在尝试测试一个 React 组件并确保当它的按钮被点击时，正确的方法被调用。但是，当我尝试运行测试并尝试监视该方法时，我收到以下消息：

错误：无法监视原始值；给定的未定义

如何测试单击按钮时是否调用了正确的方法？谢谢！

sampleComponent.jsx：

import * as React from 'react';

const SampleComponent = () => {
  const sampleMethod = () => {
    console.log('hello world');
  };

  return <button onClick={sampleMethod} type="button">Click Me</button>;
};

export default SampleComponent;

sampleComponent.test.jsx：

import * as React from 'react';
import { shallow } from 'enzyme';
import SampleComponent from './sample';

test('testing spy', () => {
  const spy = jest.spyOn(SampleComponent.prototype, 'sampleMethod');
  const wrapper = shallow(<SampleComponent />);
  wrapper.find('button').simulate('click');
  expect(spy).toHaveBeenCalled();
});

Answer 1

sample.js

import * as React from 'react';

export let util = {sampleMethod: null };

const SampleComponent = () => {
  util.sampleMethod = () => {
    console.log('hello world');
  };

  return <button onClick={sampleMethod} type="button">Click Me</button>;
};

export default SampleComponent;

sample.test.js

import { shallow } from 'enzyme';
import SampleComponent, {util} from './sample';

test('testing spy', () => {
  const spy = jest.spyOn( util, 'sampleMethod' );
  const wrapper = shallow(<SampleComponent />);
  wrapper.find('button').simulate('click');
  expect(spy).toHaveBeenCalled(1);
});

我知道我回答迟了，但我认为这也会对其他一些开发者有所帮助

Answer 2

错误的意思是，你在函数组件SampleComponent中定义的函数sampleMethod没有在SampleComponent.prototype中定义。所以SampleComponent.prototype.sampleMethod 是undefined，开玩笑不能窥探undefined 的值。

所以测试sampleMethod事件处理程序的正确方法是这样的：

index.spec.tsx:

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

describe('SampleComponent', () => {
  test('should handle click correctly', () => {
    const logSpy = jest.spyOn(console, 'log');
    const wrapper = shallow(<SampleComponent></SampleComponent>);
    const button = wrapper.find('button');
    expect(button.text()).toBe('Click Me');
    button.simulate('click');
    expect(logSpy).toBeCalledWith('hello world');
  });
});

我们可以监视console.log，判断它是否被调用。

100% 覆盖率的单元测试结果：

 PASS  src/react-enzyme-examples/02-react-hooks/index.spec.tsx
  SampleComponent
    ✓ should handle click correctly (19ms)

  console.log node_modules/jest-mock/build/index.js:860
    hello world

-----------|----------|----------|----------|----------|-------------------|
File       |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
-----------|----------|----------|----------|----------|-------------------|
All files  |      100 |      100 |      100 |      100 |                   |
 index.tsx |      100 |      100 |      100 |      100 |                   |
-----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        5.036s

依赖版本：

"react": "^16.11.0",
"enzyme": "^3.10.0",
"enzyme-adapter-react-16": "^1.15.1",
"jest": "^24.9.0",
"jest-environment-enzyme": "^7.1.1",
"jest-enzyme": "^7.1.1",