how to mock configurable middleware in node js with sinon and mocha - node.js

Question

I have configurable middleware where I can pass parameters and based on that it calls next function.
middleware code:
File: my-middleware.js
exports.authUser = function (options) {
return function (req, res, next) {
// Implement the middleware function based on the options object
next()
}
}
var mw = require('./my-middleware.js')
app.use(mw.authUser({ option1: '1', option2: '2' }))
How to mock the middleware using sinon js?
I have done in this way but, it throwing me "TypeError: next is not a function".
Here is my unit test code:
it("Should return data by id", (done: any) => {
sandbox.stub(mw, 'authUser')
.callsFake((req: any, res: any, next: any) => { return next(); });
server = require('../../index');
let req = {
"id": '123'
}
chai.request(server)
.post("/user")
.send(req)
.end((request, res) => {
expect(res.status).to.equal(200);
expect(res.body.success).to.equal(true);
done();
});
});
Can you help me to mock the configurable middleware? Thanks in advance!!

Answer 1

The authUser is a high order function, so you need to stub it for this.
E.g.
mws.js:
exports.authUser = function(options) {
return function(req, res, next) {
// Implement the middleware function based on the options object
next();
};
};
app.js:
const express = require('express');
const mws = require('./mws');
const app = express();
app.use(mws.authUser({ option1: '1', option2: '2' }));
app.post('/user', (req, res, next) => {
res.json({ success: true });
});
module.exports = app;
app.integration.test.js:
const chai = require('chai');
const chaiHttp = require('chai-http');
const sandbox = require('sinon').createSandbox();
const mws = require('./mws');
chai.use(chaiHttp);
const expect = chai.expect;
describe('61818474', () => {
afterEach(() => {
sandbox.restore();
});
it('Should return data by id', (done) => {
sandbox.stub(mws, 'authUser').callsFake((options) => (req, res, next) => {
return next();
});
const server = require('./app');
const req = { id: '123' };
chai
.request(server)
.post('/user')
.send(req)
.end((request, res) => {
expect(res.status).to.equal(200);
expect(res.body.success).to.equal(true);
sandbox.assert.calledWith(mws.authUser, { option1: '1', option2: '2' });
done();
});
});
});
integration test results with coverage report:
61818474
✓ Should return data by id (257ms)
1 passing (265ms)
----------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files | 80 | 100 | 33.33 | 80 |
app.js | 100 | 100 | 100 | 100 |
mws.js | 33.33 | 100 | 0 | 33.33 | 2-4
----------|---------|----------|---------|---------|-------------------

Answer 2

By specifying jestjs in your tags... I guess you might want to use additional functions that Jest gives you for free.
You don't really need Sinon in this case, Jest has its own way to mock/stub (entire modules too), something like jest.mock('moduleName').
You might want to check the following link for useful examples and possible usages:
https://jestjs.io/docs/en/manual-mocks