如何使用 Jest 仅为特定测试模拟模块的功能

Question

我需要模拟依赖项的功能，但仅适用于特定的测试用例。 在我的其他测试中，我想保持模块不变。 我也在嘲笑其他模块。 那些需要保持嘲笑。

我尝试了多种方法，因为已经提出了这个问题的许多变体，但是由于我需要在未模拟时使用原始模块，因此其他解决方案似乎都不起作用......

这是我需要的示例

// app.ts
import * as moduleA from 'moduleA';

// ...

app.post('/signup', async (req, res) => {
   // ...
   const hashed = await moduleA.hash(req.body.password);
   // ...
});

export default app;


// app.test.ts

// some mocks
jest.mock('./database', () => ({ ... }));
// ...

import * as request from 'supertest';
import app from './app';

// ...

describe('A', () => {
    test('Those should work', async () => {
        const response = await request(app).post('/signup').send({ password: 'pw' });
        expect(response.status).toBe(200);
        // ...
    });
    // many other tests
    
    test('I need to force hash to crash here', async () => {
        // mock moduleA.hash only for this test
        const response = request(app).post('/signup').send({ password: 'pw' });
        expect(response.status).toBe(500);
    });

    test('moduleA.hash should be back to its default function', async () => {
        // request(app) and moduleA.hash will work properly, not mocked
        // ./database stays mocked
    });
});

Answer 1

您可以使用jest.spyOn()嘲笑hash的方法moduleA ，并使用.mockRestore()恢复hash方法最初实现。

这是解决方案：

app.ts ：

import express from 'express';
import bodyParser from 'body-parser';

import * as moduleA from './moduleA';
const app = express();

app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());

app.post('/signup', async (req, res) => {
  try {
    const hashed = await moduleA.hash(req.body.password);
    console.log(hashed);
    res.sendStatus(200);
  } catch (error) {
    res.sendStatus(500);
  }
});

export default app;

moduleA.ts ：

export const hash = async (data: string) => {
  return 'real hashed value';
};

app.spec.ts ：

import app from './app';
import request from 'supertest';
import * as moduleA from './moduleA';

describe('app', () => {
  test('Those should work', async () => {
    const response = await request(app)
      .post('/signup')
      .send({ password: 'pw' });
    expect(response.status).toBe(200);
  });

  test('I need to force hash to crash here', async () => {
    const mockedError = new Error('hash error');
    const hashSpy = jest.spyOn(moduleA, 'hash').mockRejectedValueOnce(mockedError);
    const response = await request(app)
      .post('/signup')
      .send({ password: 'pw' });
    expect(response.status).toBe(500);
    expect(moduleA.hash).toBeCalledWith('pw');
    hashSpy.mockRestore();
  });

  test('moduleA.hash should be back to its default function', async () => {
    const logSpy = jest.spyOn(console, 'log');
    const response = await request(app)
      .post('/signup')
      .send({ password: 'pw' });
    expect(response.status).toBe(200);
    expect(logSpy).toBeCalledWith('real hashed value');
  });
});

100% 覆盖率的单元测试结果：

PASS  src/stackoverflow/47540126/app.spec.ts
  app
    ✓ Those should work (72ms)
    ✓ I need to force hash to crash here (10ms)
    ✓ moduleA.hash should be back to its default function (14ms)

  console.log src/stackoverflow/47540126/app.ts:3569
    real hashed value

  console.log node_modules/jest-mock/build/index.js:860
    real hashed value

------------|----------|----------|----------|----------|-------------------|
File        |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
------------|----------|----------|----------|----------|-------------------|
All files   |      100 |      100 |      100 |      100 |                   |
 app.ts     |      100 |      100 |      100 |      100 |                   |
 moduleA.ts |      100 |      100 |      100 |      100 |                   |
------------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       3 passed, 3 total
Snapshots:   0 total
Time:        4.156s, estimated 5s

这是完整的演示： https : //github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/47540126