引入单元测试工具Jest

$ npm install jest ts-jest @types/jest -D

$ npx ts-jest config:init

/** @type {import('ts-jest/dist/types').InitialOptionsTsJest} */
module.exports = {
  preset: 'ts-jest',
  testEnvironment: 'node',
  transform: { "^.+\\.ts?$": "ts-jest" },
  moduleFileExtensions: ["ts", "tsx", "js", "jsx", "json", "node"]
};

{
    test: "jest"
    // 如果要测试覆盖率，后面加上--coverage
    // 如果要监听所有测试文件 --watchAll
}

export function sum(a: number, b: number) {
    return a + b;
}

import { sum } from './a';

test('adds 1 + 2 to equal 3', () => {
    expect(sum(1, 2)).toBe(3);
});

$ npx jest

export function sum(a: number, b: number) {
    return a + a;
}

test('two plus two is four', () => {
    expect(2 + 2).toBe(4);
});

const fethUserInfo = fetch('http://xxxx')

// fetchData.test.js

// 测试promise成功需要加.resolves方法
test('the data is peanut butter', async () => {
    await expect(fethUserInfo()).resolves.toBe('peanut butter');
});

// 测试promise成功需要加.rejects方法
test('the fetch fails with an error', async () => {
    await expect(fethUserInfo()).rejects.toMatch('error');
});

// 分组一
describe('Test xxFunction', () => {
  test('Test default return zero', () => {
      expect(xxFunction()).toBe(0)
  })

  // ...其它test
})

// 分组二
describe('Test xxFunction2', () => {
  test('Pass 3 can return 9', () => {
      expect(xxFunction2(3)).toBe(9)
  })

  // ...其它test
})

export default class compute {
    constructor() {
        this.number = 0
    }
    addOne() {
        this.number += 1
    }
    addTwo() {
        this.number += 2
    }
    minusOne() {
        this.number -= 1
    }
    minusTwo() {
        this.number -= 2
    }
}

import compute from './index'

const Compute = new compute()

test('测试 addOne', () => {
    Compute.addOne()
    expect(Compute.number).toBe(1)
})

test('测试 minusOne', () => {
    Compute.minusOne()
    expect(Compute.number).toBe(0)
})

// 模拟数据库
const userDB = [
    { id: 1, name: '小明' },
    { id: 2, name: '小花' },
]

// 新增数据
const insertTestData = data => {
    // userDB,push数据
}

// 删除数据
const deleteTestData = id => {
    // userDB,delete数据
}

// 全部测试完
afterAll(() => {
    console.log(userDB)
})

describe('Test about user data', () => {

  beforeAll(() => {
      insertTestData({ id: 99, name: 'CS' })
  })
  afterAll(() => {
      deleteTestData(99)
  })

})

export const data2 = () => {
    return {
        name: 'zhangsan',
        age: 26,
        time: new Date()
    }
}

import { data2 } from "./index"

it('测试快照 data2', () => {
    expect(data2()).toMatchSnapshot({
        name: 'zhangsan',
        age: 26,
        time: expect.any(Date) //用于声明是个时间类型，否则时间会一直改变，快照不通过
    })
})

import React from 'react';
function Counter(){
    return (
        <ul>
            <li>
                <button id='counter1' className='button1'>counter1</button>
            </li>
            <li>
                <button id='counter2' className='button2'>counter2</button>
            </li>
        </ul>
    )
}

import Counter from 'xx';
import { mount } from 'enzyme';

describle('测试APP',() => {
    test('用户进入首页，看到两个按钮，分别是counter1和counter2,并且按钮文字也是counter1和counter2',()=>{
        const wrapper = mount(<Counter />);
        const button = wrapper.find('button');
        except(button).toHaveLength(2);
        except(button.at(0).text()).toBe('counter1');
        except(button.at(1).text()).toBe('counter2');
    })
})