如何用Jest模拟外部模块的功能 [英] How to mock an external module's function with Jest

问题描述

Jest的模拟可以处理我未编写的模块中的功能吗?

Can Jest's mocking handle functions from modules I didn't write?

node-yelp-api-v3 具有Yelp.searchBusiness(String)，但是我尝试使用 Jest的模拟功能失败. Jest示例似乎假设我正在模拟项目中具有的模块.从文档中，我还不清楚如何在模块中模拟特定功能.

node-yelp-api-v3 has Yelp.searchBusiness(String) but my attempts to use Jest's mocking functionality are unsuccessful. The Jest examples seem to assume that I'm mocking a module I have in the project. From the documentation I'm also unclear how to mock a specific function in a module.

这些都不起作用:

jest.mock('Yelp.searchBusiness', () => {
  return jest.fn(() => [{<stubbed_json>}])
})

或

jest.mock('Yelp', () => {
  return jest.fn(() => [{<stubbed_json>}])
})

我当前正在使用sinon，但只想使用Jest.希诺这种方法有效:

I'm currently using sinon but would like to use just Jest. This Sinon approach works:

var chai = require('chai')
var should = chai.should()
var agent = require('supertest').agent(require('../../app'))

const Yelp = require('node-yelp-api-v3')

var sinon = require('sinon')
var sandbox

describe('router', function(){
  beforeEach(function(){
    sandbox = sinon.sandbox.create()
    stub = sandbox.stub(Yelp.prototype, 'searchBusiness')
  })

  afterEach(function(){
    sandbox.restore()
  })

  it ('should render index at /', (done) => {
    /* this get invokes Yelp.searchBusiness */
    agent
      .get('/')
      .end(function(err, res) {
        res.status.should.equal(200)
        res.text.should.contain('open_gyro_outline_500.jpeg')

        done()
      })
  })
})

推荐答案

模拟外部模块的说明此处.

如果您要模拟的模块是节点模块(例如:lodash)，则模拟应放置在与node_modules相邻的__mocks__目录中(除非您将根配置为指向除项目根目录)，并将被自动嘲笑.无需显式调用jest.mock('module_name').

If the module you are mocking is a Node module (e.g.: lodash), the mock should be placed in the __mocks__ directory adjacent to node_modules (unless you configured roots to point to a folder other than the project root) and will be automatically mocked. There's no need to explicitly call jest.mock('module_name').

对于您的确切情况，这意味着您需要创建其中包含文件node-yelp-api-v3.js的文件夹__mocks__.在该文件中，您可以使用 genMockFromModule 从原始模块中创建一个模拟对象.并覆盖您要模拟的方法.

For your exact case this would mean you need to create a folder __mocks__ with a file node-yelp-api-v3.js in it. In that file you create a mock object from the original module using genMockFromModule and override the method you want to mock.

// __mocks__/node-yelp-api-v3.js

const yelp = jest.genMockFromModule('node-yelp-api-v3')

function searchBusiness() {
    return [{<stubbed_json>}]
}

yelp.searchBusiness = searchBusiness

module.exports = yelp

此外，如果以后要为该方法调用像searchBusiness.mock.calls.length这样的断言，也可以将searchBusiness包装在jest.fn中.

Additionally you could also wrap the searchBusiness in jest.fn if you want to call assertions like searchBusiness.mock.calls.length for this method later.

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