nodejs - stub module.exports functions with sinon

Question

I have an expressjs app with the following routes and middleware modules. I am trying to test the routes module using mocha, chai, http-chai and sinonjs. The API uses mysql and in order to test the routes module, I have it all modularized so that I can stub out the mysql module. However when I try to stub middleware/index, I am having trouble. If I try to require index normally, the module doesn't actually get stubbed. If I try to require it using require.cache[require.resolve('./../../lib/routes/middleware/index')];, it seems to stub something, but indexStub.returns(indexObj) returns an error TypeError: indexStub.returns is not a function and TypeError: indexStub.restore is not a function.

How do I stub out index.js properly in order to control the code flow and keep it from trying to connect to mysql?

routes.js

'use strict';

const express =      require('express');
const router =       express.Router();
const configs =      require('./../config/configs');
const middleware =   require('./middleware/index');
const bodyParser =   require('body-parser');

const useBodyParserJson = bodyParser.json({
  verify: function (req, res, buf, encoding) {
    req.rawBody = buf;
  }
});

const useBodyParserUrlEncoded = bodyParser.urlencoded({extended: true});

// creates a new post item and return that post in the response
router.post('/posts', useBodyParserUrlEncoded, useBodyParserJson, middleware.validatePostData, middleware.initializeConnection, middleware.saveNewPost, middleware.closeConnection, function(req, res) {
  if (res.statusCode === 500) {
    return res.send();
  }
  if (res.statusCode === 405) {
    return res.send('Item already exists with slug ' + req.body.slug + '. Invalid method POST');
  }
  res.json(res.body).end();
});

module.exports = router;

middleware/index.js

'use strict';

const configs =  require('./../../config/configs');
const database = require('./../../factories/databases').select(configs.get('STORAGE'));
const dataV = require('./../../modules/utils/data-validator');


module.exports = {
  initializeConnection: database.initializeConnection, // start connection with database
  closeConnection:      database.closeConnection,      // close connection with database
  saveNewPost:          database.saveNewPost,          // creates and saves a new post
  validatePostData:     dataV.validatePostData,        // validates user data
};

spec-routes.js

'use strict';

var chai = require('chai');
var chaiHttp = require('chai-http');
var sinonChai = require("sinon-chai");
var expect = chai.expect;
var sinon = require('sinon');
chai.use(sinonChai);
chai.use(chaiHttp);
var app = require('./../../app');

  describe('COMPLEX ROUTES WITH MIDDLEWARE', function() {
    var indexM = require.cache[require.resolve('./../../lib/routes/middleware/index')];

    describe('POST - /posts', function() {
      var indexStub,
        indexObj;

      beforeEach(function() {
        indexStub = sinon.stub(indexM);
        indexObj = {
          'initializeConnection': function(req, res, next) {
            return next();
          },
          'closeConnection': function(req, res, next) {
            return next();
          },
          'validatePostData': function(req, res, next) {
            return next();
          }
        };
      });

      afterEach(function() {
        indexStub.restore();
      });

      it('should return a 500 response', function(done) {
        indexObj.saveNewPost = function(req, res, next) {
          res.statusCode = 500;
          return next();
        };
        indexStub.returns(indexObj);
        chai.request(app)
          .post('/posts')
          .send({'title': 'Hello', 'subTitle': 'World', 'slug': 'Example', 'readingTime': '2', 'published': false})
          .end(function(err, res) {
            expect(res).to.have.status(500);
            done();
          });
      });
    });
  });

Answer 1

You don't use Sinon at all, as it doesn't deal with module loading at all. I see you have started doing this manually using the internal Node API's, but I suggest you do it the way we advise in the Sinon docs regarding this usecase: juse use proxyquire.

It enables you to substitute require calls to ./middleware/index.js for a mock object of your own liking (possibly made using sinon).

You would use it something like this:

var myIndex = { 
  initializeConnection: sinon.stub(),
  closeConnection:      sinon.stub(),
  saveNewPost:          sinon.stub()
};
var app = proxyquire('./../../app', {'./middleware/index': myIndex});