Cannot mock passport authenticate('local') method with sinon

Question

I'm trying to mock the passport.authenticate('local'):

 app.post('/login', passport.authenticate('local'), (req, res, next) => {console.log('should enter');})

Am using Sinon, but the method doesn't execute the console.log inside the login route

beforeEach(function (done) {
      aut = sinon.stub(server.passport, 'authenticate').returns(() => {});
      server.app.on('appStarted', function () {
        done();
      });
    });

afterEach(() => {
  aut.restore();
});

describe('Login', () => {
  it('should login', (done) => {
    chai.request(server.app)
      .post('/login')
      .send({
        username: 'user',
        password: 'pas'
      })
      .end(function (error, response, body) {
        return done();
      });
  });
});

Also, When I put the mock inside the real passport.authenticate('local') like this:

app.post('/login', () => {}, (req, res, next) => {console.log('should enter');})

It still doesn't enter the route which means that the sinon callFake wouldn't help at all. Only if I remove the

passport.authenticate('local')

from the /login route will the 'should login' test enter the route.

Implement sinon in beforeEach

let server = require('../../../app.js');
let expect = chai.expect;
chai.use(chaiHttp);

var aut;
beforeEach(() => {
  aut = sinon.stub(server.passport, 'authenticate').returns((req, res, next) => next());
});

app.js

const app = express();

middleware.initMiddleware(app, passport);

const dbName = 'dbname';
const connectionString = 'connect string';

mongo.mongoConnect(connectionString).then(() => {
        console.log('Database connection successful');
        app.listen(5000, () => console.log('Server started on port 5000'));
    })
    .catch(err => {
        console.error('App starting error:', err.stack);
        process.exit(1);
    });

// If the Node process ends, close the Mongoose connection
process.on('SIGINT', mongo.mongoDisconnect).on('SIGTERM', mongo.mongoDisconnect);

register.initnulth(app);

login.initfirst(app, passport);
logout.initsecond(app);


module.exports = app;

Answer 1

It seems you want to use a middleware callback that does nothing but just lets the request be handled by later middlewares. Such callback would be:

(req, res, next) => next()

The middleware has to call next() for the request continue being processed by later middlewares. So you should setup your stub like this:

aut = sinon.stub(server.passport, 'authenticate').returns((req, res, next) => next());