如何在 node.js 单元测试中模拟构造函数调用？答案

【问题标题】：How to mock a constructor call in a node.js unit test?如何在 node.js 单元测试中模拟构造函数调用？
【发布时间】：2021-09-29 07:41:09
【问题描述】：

我编写了一个小的 node.js 模块来使用 Twit 库更新 twitter

// src/twitterHelper.js
const Twit = require('twit');
const twitterClient = new Twit({
  consumer_key: 'consumer_key',
  consumer_secret: 'consumer_secret',
  access_token: 'access_token',
  access_token_secret: 'access_token_secret',
});

function updateStatus(params, callback) {
  twitterClient.post('statuses/update', params, function (err, data, response) {
    if (err) {
      console.log(`Error occurred updating status\t${err}`);
    } else {
      console.log(`Posted twitter with id ${data.id_str}`);
    }
  });
}

exports.updateStatus = updateStatus;

我已经为此使用 mocha、chai 和 sinon 编写了一个单元测试。但是对 Twit 的构造函数的调用总是返回实际对象 - 我如何用单元测试中的模拟对象替换它？

// test/twitterHelper.spec.js
const Twit = require('twit')
const expect = require("chai").expect;
const sinon     = require('sinon');
const twitterHelper = require("../src/twitterHelper");

describe("Unit tests for twitter helper", () => {
    const mockTwit = {
        post: (endpoint, params, callback) => {
            console.log(`Called ${endpoint} with ${params}`);
        }
    };

    it("should create a mock twit object", () => { 
        sinon.stub(Twit, 'constructor').returns(mockTwit);
        twitterHelper.updateStatus({status: "New status"});
    });
});

【问题讨论】：

标签： node.js unit-testing mocha.js chai sinon

【解决方案1】：

Sinon 不支持这样的类的存根构造函数。你需要使用Link Seams，这是CommonJS版本，所以我们将使用proxyquire来构造我们的接缝。

例如

twitterHelper.js:

const Twit = require('twit');
const twitterClient = new Twit({
  consumer_key: 'consumer_key',
  consumer_secret: 'consumer_secret',
  access_token: 'access_token',
  access_token_secret: 'access_token_secret',
});

function updateStatus(params, callback) {
  twitterClient.post('statuses/update', params, function (err, data, response) {
    if (err) {
      console.log(`Error occurred updating status\t${err}`);
    } else {
      console.log(`Posted twitter with id ${data.id_str}`);
    }
  });
}

exports.updateStatus = updateStatus;

twitterHelper.test.js:

const sinon = require('sinon');
const proxyquire = require('proxyquire');

describe('Unit tests for twitter helper', () => {
  it('should create a mock twit object', () => {
    const twitInstanceStub = { post: sinon.stub() };
    const TwitStub = sinon.stub().returns(twitInstanceStub);
    const twitterHelper = proxyquire('./twitterHelper', {
      twit: TwitStub,
    });
    twitterHelper.updateStatus({ status: 'New status' });
    sinon.assert.calledWithExactly(TwitStub, {
      consumer_key: 'consumer_key',
      consumer_secret: 'consumer_secret',
      access_token: 'access_token',
      access_token_secret: 'access_token_secret',
    });
    sinon.assert.calledWithExactly(
      twitInstanceStub.post,
      'statuses/update',
      { status: 'New status' },
      sinon.match.func,
    );
  });
});

测试结果：

  Unit tests for twitter helper
    ✓ should create a mock twit object (1506ms)


  1 passing (2s)

------------------|---------|----------|---------|---------|-------------------
File              | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
------------------|---------|----------|---------|---------|-------------------
All files         |   57.14 |        0 |      50 |   57.14 |                   
 twitterHelper.js |   57.14 |        0 |      50 |   57.14 | 11-14             
------------------|---------|----------|---------|---------|-------------------

【讨论】：