错误发现得越早，改正错误的成本越低，正确改正错误的可能性也越大。 —— 《软件测试的艺术》

基础配置

yarn add --dev jest typescript ts-jest @types/jest

基本用法

代码：

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

单个用例

// single test
test('1+2=3', () => {
  let num = sum(1, 2);
  expect(num).toEqual(3);
});

yarn jest运行结果：

 PASS  src/__tests__/math.test.ts
  ✓ 1+2=3 (3 ms)

多个用例组合：describe + test

// multiple tests
describe('sum', () => {
  test('1+2=3', () => {
    let num = sum(1, 2);
    expect(num).toEqual(3);
  });
  test('11+12=23', () => {
    let num = sum(11, 12);
    expect(num).toEqual(23);
  });
});

yarn jest运行结果：

 PASS  src/__tests__/math.test.ts
  sum
    ✓ 1+2=3 (2 ms)
    ✓ 11+12=23

用例运行前后 hook 设置：Setup and Teardown

hooks：

• beforeEach

• afterEach

• beforeAll

• afterAll

作用域：文件或 describe 内

执行顺序：用例+hooks 组合场景

• 按文件顺序执行 describe 内同步代码

• 按文件顺序执行执行 test 单测：

  • beforeAll（作用域内执行一次）
  • beforeEach
  • test 单测
  • afterEach
  • afterAll（作用域内执行一次）

示例：order-of-exec.test.ts

beforeAll(() => console.log('1 - beforeAll'));
afterAll(() => console.log('1 - afterAll'));
beforeEach(() => console.log('1 - beforeEach'));
afterEach(() => console.log('1 - afterEach'));

test('', () => console.log('1 - test'));

describe('Scoped / Nested block', () => {
  console.log('describe----------');
  beforeAll(() => console.log('2 -- beforeAll'));
  afterAll(() => console.log('2 -- afterAll'));
  beforeEach(() => console.log('2 -- beforeEach'));
  afterEach(() => console.log('2 -- afterEach'));

  test('', () => console.log('2 -- test'));
});


// 执行结果：
// describe----------
// 1 - beforeAll
// 1 - beforeEach
// 1 - test
// 1 - afterEach
// 2 - beforeAll
// 1 - beforeEach
// 2 - beforeEach
// 2 - test
// 2 - afterEach
// 1 - afterEach
// 2 - afterAll
// 1 - afterAll

建议：do setup and teardown inside before* and after* handlers rather than inside the describe blocks.

skip and only

一般用于验证和调试

skip:

describe('skip', () => {
  test('should be ok', () => {
    expect(3).toEqual(3);
  });
  // skip 的会被跳过
  test.skip('skip', () => {
    expect(3).toEqual(3);
  });
});

执行结果：

 PASS  src/__tests__/skip.test.ts
  skip
    ✓ should be ok (2 ms)
    ○ skipped skip

only:

describe('only', () => {
  // 只有 only 的会执行
  test.only('should be ok', () => {
    expect(3).toEqual(3);
  });
  test('skip', () => {
    expect(3).toEqual(3);
  });
});

执行结果：

 PASS  src/__tests__/only.test.ts
  only
    ✓ should be ok (2 ms)
    ○ skipped skip

进阶用法

异步

async function getDataByAsync() {
  await new Promise((res) => setTimeout(res, 1 * 100));
  return 3;
}

describe('getDataByAsync', () => {
  // test 的 fn 参数传入一个 异步函数, hooks 也能这么用
  test('data should be 3', async () => {
    let data = await getDataByAsync(); // 记得 await
    expect(data).toEqual(3);
  });
});

Error

同步方法

function funcThantThrowError() {
  throw new Error('something wrong');
}

test('funcThantThrowError', () => {
  // 参数为函数名
  expect(funcThantThrowError).toThrow('something wrong');
  // 带参数的写法: 若 funcThantThrowError 带参数
  expect(() => funcThantThrowError(1，2，3)).toThrow('something wrong');
});

异步方法

async function funcThantThrowErrorByAsync() {
  await new Promise((res) => setTimeout(res, 1 * 100));
  throw new Error('something wrong by async');
}

// method 1
test('test funcThantThrowErrorByAsync with try catch', async () => {
  try {
    await funcThantThrowErrorByAsync();
  } catch (error) {
    expect(error).toEqual(new Error('something wrong by async'));
  }
});

// method 2
test('test funcThantThrowErrorByAsync with rejects', async () => {
  await expect(funcThantThrowErrorByAsync).rejects.toThrow(
    'something wrong by async'
  );
});

Mock

函数

function forEach(n: number, callback: Function) {
  for (let index = 0; index < n; index++) {
    callback(index);
  }
}
test('forEach', () => {
  const mockCallback = jest.fn((x) => 42 + x);
  forEach(2, mockCallback);

  // The mock function is called twice
  expect(mockCallback.mock.calls.length).toBe(2);

  // The first argument of the first call to the function was 0
  expect(mockCallback.mock.calls[0][0]).toBe(0);

  // The first argument of the second call to the function was 1
  expect(mockCallback.mock.calls[1][0]).toBe(1);

  // The return value of the first call to the function was 42
  expect(mockCallback.mock.results[0].value).toBe(42);

  // The return value of the second call to the function was 43
  expect(mockCallback.mock.results[1].value).toBe(43);
});

参考：https://jestjs.io/docs/mock-function-api

类中的方法

使用spyOn

class DataProvider {
  getDataById(id: string) {
    return `mock data ${id}`;
  }
}

function getData(id: string) {
  let provider = new DataProvider();
  return provider.getDataById(id);
}

describe('getData', () => {
  test('should pass', () => {
    // mock DataProvider 的 getDataById 方法
    const spy = jest
      .spyOn(DataProvider.prototype, 'getDataById')
      .mockImplementation((id: string): string => {
        return `spy mock data ${id}`;
      });

    let data = getData('11');
    expect(data).toBe('spy mock data 11');

    // 清除 mock，否则 下个用例会失败，一般清理操作会放到 hook 中
    spy.mockRestore();
  });
  test('should fail if spy is enabled', () => {
    let data = getData('11');
    expect(data).toBe('mock data 11');
  });
});

普通模块

src/async-data-provider.ts:

export async function getDataByAsync() {
  await new Promise((res) => setTimeout(res, 1 * 100));
  return 3;
}

export async function getDataById(id: string) {
  await new Promise((res) => setTimeout(res, 1 * 100));
  return `mock data ${id}`;
}

方法1：参考「类中的方法」的 spyOn

import * as provider from '../async-data-provider';

test('getDataById', async () => {
  const spy = jest
    .spyOn(provider, 'getDataById')
    .mockImplementation(async (id: string) => {
      return `spy mock data ${id}`;
    });

  let data = await provider.getDataById('11');
  expect(data).toBe('spy mock data 11');

  spy.mockRestore();
});

方义2：

mock 文件：src/__mocks__/async-data-provider.ts

export async function getDataById(id: string) {
  await new Promise((res) => setTimeout(res, 1 * 100));
  return `mock mock data ${id}`;
}

测试文件：src/__tests__/mock-module-with-mock.test.ts

import * as provider from '../async-data-provider';

jest.mock('../async-data-provider');

test('getDataById', async () => {
  let data = await provider.getDataById('11');
  expect(data).toBe('mock mock data 11');
});

node_modules 中的模块

• 需要在 jest 配置中的roots目录下，创建__mocks__文件夹

• 模块命名规则：__mocks__/@scope/project-name.ts

Mock 文件：src/__mocks__/lodash.ts

function nth<T>(items: T[], n: number) {
  console.log('mock lodash-----');
  return items[n];
}
let _ = { nth };
export default _;

测试文件：src/__tests__/mock-npm-module.test.ts

import _ from 'lodash';

test('mock nth', async () => {
  let items = [0, 1, 2];
  let n = _.nth(items, 2);
  expect(n).toBe(2);
});

执行结果:

    mock lodash-----
 PASS  src/__tests__/mock-npm-module.test.ts
  ✓ mock nth (19 ms)

其它：mock 万物

Todo: mysql，mongodb，redis，mq...

jest.requireActual

其他

覆盖率

细化统计

命令：yarn jest --coverage --silent

------------------------|---------|----------|---------|---------|-------------------
File                    | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
------------------------|---------|----------|---------|---------|-------------------
All files               |      25 |      100 |       0 |   33.33 |                   
 async-data-provider.ts |      25 |      100 |       0 |   33.33 | 2-3               
------------------------|---------|----------|---------|---------|-------------------

汇总统计

命令：yarn jest --coverage --silent --coverageReporters="text-summary"

=============================== Coverage summary ===============================
Statements   : 25% ( 1/4 )
Branches     : 100% ( 0/0 )
Functions    : 0% ( 0/2 )
Lines        : 33.33% ( 1/3 )
================================================================================

expect 源码

jest/packages/expect/src/index.ts:

export const expect: Expect = (actual: any, ...rest: Array<any>) => {
  if (rest.length !== 0) {
    throw new Error('Expect takes at most one argument.');
  }

  const allMatchers = getMatchers();
  const expectation: any = {
    not: {},
    rejects: {not: {}},
    resolves: {not: {}},
  };

  const err = new JestAssertionError();

  Object.keys(allMatchers).forEach(name => {
    const matcher = allMatchers[name];
    const promiseMatcher = getPromiseMatcher(name, matcher) || matcher;
    expectation[name] = makeThrowingMatcher(matcher, false, '', actual);
    expectation.not[name] = makeThrowingMatcher(matcher, true, '', actual);

    expectation.resolves[name] = makeResolveMatcher(
      name,
      promiseMatcher,
      false,
      actual,
      err,
    );
    expectation.resolves.not[name] = makeResolveMatcher(
      name,
      promiseMatcher,
      true,
      actual,
      err,
    );

    expectation.rejects[name] = makeRejectMatcher(
      name,
      promiseMatcher,
      false,
      actual,
      err,
    );
    expectation.rejects.not[name] = makeRejectMatcher(
      name,
      promiseMatcher,
      true,
      actual,
      err,
    );
  });

  return expectation;
};

参考

• Getting Started · Jest

• Unit Testing Guidelines