开玩笑地使用 spyOn 模拟嵌套的 function，但仍然调用实际的 function

Question

getInfo calls getColor in the same file. My intention is to mock getColor function, I import the func.js as a module and spyOn getColor . The mocked getColor is supposed to return "Red", but it still calls the actual function and returns "Black".

Function File

// func.js
function getColor() {
    return "black"
}

function getInfo(){
    const color = getColor()
    const size = "L"
    return `${color}-${size}`
}

module.exports = { getColor, getInfo }

Test File

// func.test.js
const func = require("./func")

describe("Coverage Change Test", () => {
  beforeAll(() => {
    const colorMock = jest.spyOn(func, "getColor"); // spy on otherFn
    colorMock.mockImplementation(() => "Red");
  });

  afterAll(() => {
    colorMock.resetAllMocks();
  })

  test("return Large Red", async () => {
    const res = func.getInfo();
    expect(res).toEqual("Red-L");
  });
});

I also tried requireActual , but it also calls the actual one.

const { getInfo, getColor } = require('./func');

jest.mock('./func', () => ({
  ...jest.requireActual('./func.'),
  getColor: jest.fn().mockImplementation(() => 'Red'),
}))

describe('test', () => {
  test('returns red', () => {
    const res = getInfo()
    expect(res).toEqual("Red-L")
  })
})

How can I properly mock up a nested function in Jest? Thanks in advance.

Answer 1

You're spying on func.getColor and mocking its implementation but getInfo is calling the locally scoped getColor function. You have to change the way getColor is being called to be able to mock it.

exports.getColor = function() {
  return 'black'
}

exports.getInfo = function() {
  const color = exports.getColor()
  const size = 'L'
  return `${color}-${size}`
}

Answer 2

Use rewire module to rewrite your exported properties.

Your test file will look like this:

const rewire = require('rewire')

describe('test', () => {
  let func;
  let getColorSpy;
  beforeEach(() => {
    getColorSpy = jest.fn()
    func = rewire(__dirname + '/func.js') // import
    func.__set__('getColor', getColorSpy) // rewrite content of getColor
  })
  test('should return Red-L when getColor returns Red', () => {
    getColorSpy.mockReturnValue('Red')

    const res = func.getInfo()

    expect(res).toEqual("Red-L")
  })
})

Try to avoid write code like your module.