检查通过 rewire 可见的（私有/非导出）函数上的方法调用

Question

我有一个只有一个导出函数和几个非导出函数的模块来保持 api“干净”。我正在尝试使用 jest & require 编写单元测试，但出现以下错误：

Error: expect(jest.fn())[.not].toBeCalledTimes()
    jest.fn() value must be a mock function or spy.
Received:
    function: [Function doMagic]

如果我尝试进行间谍活动，我如何才能获得通过rewire （或其他验证方法被调用频率的其他方式）可见的非导出方法的监视，尽管能够在最后一次测试中调用函数如下所示：Cannot spy the doMagic property because it is not a function; undefined given instead

我的场景的简单示例： 例如functions.js

const moreFunctions = require("./moreFunctions");

const theExportedFunction = someNumber => {
  return doMagic(someNumber);
};

function doMagic(someNumber) {
  if (someNumber % 2 === 0) {
    return moreFunctions.getTrue();
  }
  return moreFunctions.getFalse();
}

module.exports = { theExportedFunction };

其他模块： moreFunctions.js

const moreFunctions = {
  getTrue: () => true,
  getFalse: () => false
};

module.exports = moreFunctions;

我是如何测试它的： functions.test.js

const rewire = require("rewire");

const functions = rewire("./functions");
const moreFunctions = functions.__get__('moreFunctions');

const doMagic = functions.__get__('doMagic');

const getFalse = jest.spyOn(moreFunctions, 'getFalse');
const getTrue = jest.spyOn(moreFunctions, 'getTrue');

describe("testing inner functions ", () => {

  afterEach(() => {
    jest.clearAllMocks();
  });

  test('theExportedFunction calls doMagic with 1 returns false and does not call getTrue', () => {
    const result = functions.theExportedFunction(1);
    console.log('result: ' + result);
    expect(result).toBe(false);

    //expect(doMagic).toBeCalledTimes(1);  // this blows up
    expect(getTrue).toHaveBeenCalledTimes(0);
    expect(getFalse).toHaveBeenCalledTimes(1);
  });

  test('theExportedFunction calls doMagic with 2 returns true and does not call getFalse', () => {
    const result = functions.theExportedFunction(2);
    console.log('result: ' + result);
    expect(result).toBe(true);

    //expect(doMagic).toBeCalledTimes(1); // this blows up
    expect(getTrue).toHaveBeenCalledTimes(1);
    expect(getFalse).toHaveBeenCalledTimes(0);
  });

  // This works!
  test('just testing to see if i can call the doMagic function', () => {
    const result = doMagic(2);
    expect(result).toBe(true);

    expect(getTrue).toHaveBeenCalledTimes(1);
    expect(getFalse).toHaveBeenCalledTimes(0);
  });
});

Answer 1

根据您的代码，您应该能够模拟所有并测试theExportedFunction，如下所示：

const mockGetTrue = jest.fn().mockReturnValue(true); // this name MUST start with mock prefix
const mockGetFalse = jest.fn().mockReturnValue(false); // this name MUST start with mock prefix
jest.spyOn('my_more_functions_path', () => ({
  getTrue: mockGetTrue,
  getFalse: mockGetFalse
}));
// here import the file you are testing, after the mocks! 
// for example
import {theExportedFunction} from 'my_path';

describe('theExportedFunction', () => {
  it('should call getTrue of moreFunctions', () => {
    theExportedFunction(4);
    expect(mockGetTrue).toHaveBeenCalled();
    expect(mockGetFalse).not.toHaveBeenCalled();
  });


  it('should call getFalse of moreFunctions', () => {
    theExportedFunction(5);
    expect(mockGetFalse).toHaveBeenCalled();
    expect(mockGetTrue).not.toHaveBeenCalled();
  });
});