jestjs - 开 Jest : how to mock a function which is used by another function of the same module

Question

我正在尝试测试一个依赖于同一模块中另一个函数的函数。我想模拟第二个，我尝试过的方法如下:

utils.js:

const buildEngine = () => 'Engine';

const buildCar = () => {
  const engine = buildEngine();
  return engine + ' and ' + 'Car Body';
};

module.exports = {
  buildEngine,
  buildCar
};

utils.spec.js:

function mockModule() {
  const original = require.requireActual('./utils');
  return { ...original, buildEngine: jest.fn(() => 'Mock Engine') };
}

it('Builds a Car', () => {
  jest.mock('./utils', () => mockModule());

  const utils = require.requireMock('./utils');

  expect(utils.buildEngine()).toBe('Mock Engine');
  expect(utils.buildCar()).toBe('Mock Engine and Car Body');
});

发生的情况是，即使我能够模拟“buildEngine”函数，当我测试“buildCar”函数时，它仍然引用未模拟的“buildEngine”。 请帮忙。

Answer 1

解决方案如下:

utils.js:

const buildEngine = () => 'Engine';

const buildCar = () => {
  const engine = exports.buildEngine();
  return engine + ' and ' + 'Car Body';
};

exports.buildEngine = buildEngine;
exports.buildCar = buildCar;

utils.spec.js:

const utils = require('./utils');

describe('utils', () => {
  it('Builds a Car', () => {
    const buildEngineSpy = jest.spyOn(utils, 'buildEngine').mockReturnValue('Mock Engine');
    expect(utils.buildCar()).toBe('Mock Engine and Car Body');
    expect(buildEngineSpy).toBeCalledTimes(1);
    buildEngineSpy.mockRestore();
  });

  it('build engine original implementation', () => {
    expect(utils.buildEngine()).toBe('Engine');
    expect(utils.buildCar()).toBe('Engine and Car Body');
  });
});

单元测试结果:

 PASS  src/stackoverflow/46437290/utils.spec.js
  utils
    ✓ Builds a Car (4ms)
    ✓ build engine original implementation (1ms)

Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        1.908s, estimated 2s

这是已完成的演示:https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/46437290