How can I test authentication middleware with Jest - node.js

Question

I'm learning nodejs and for the most part its going well. Im trying to learn how to do mocking in tests with jest. I've watched numerous tutorials but I cant seem to get my head around it.
I have this middleware that is used on protected routes...
import jwt from 'jsonwebtoken';
export default function (req, res, next) {
const token = req.header('x_auth-token');
if (!token) return res.status(401).json({ message: 'Access denied' });
try {
const verified = jwt.verify(token, process.env.TOKEN_SECRET);
req.user = verified;
next();
} catch (err) {
return res.status(400).send('Invalid Token');
}
}
From what I've read, I think the approach Im supposed to to take is something like this...
import verifyToken from '../middleware/verifyToken';
test('verifyToken', () => {
expect.assertions(1);
const res = {};
const req = {};
const next = (err) => expect(err).toBeFalsy();
verifyToken(req, res, next);
});
However this clearly doesnt work.
So how do I mock the request header with a token?

Answer 1

So if we comletely forget about what req, res are in the real world, obviously they are request and response, but lets just forget about that for now.
in your real code you have token = req.header("x_auth-token")
So in our test code, we need to have something in the req object that when called with those parameters returns what you want.
So I would say.
const req = {
header: jest.fn(() => 'myAuthToken')
}
the jest.fn() has mad a mock function and when it is invoked it will always return the string myAuthToken.
We can then check that the header function has been called with the correct params by adding
expect(req.header).toHaveBeenCalledWith("x_auth-token")
You are also going to need to mock jwt.verify as you are not testing that jwt.verify works as that will be covered it its own tests. You will want to make sure that you are using the response of that correctly
To do that take a look at this stack overflow question
And finally I would set next as a mock function
mockNext = jest.fn()
Then we can say in the test
expect(mockNext).toHaveBeenCalled()

Answer 2

So I was having trouble understandin how to mock functions. I did a bunch of googling based on on Ollie Pugh's answer and this is what I came up with.
import jwt from 'jsonwebtoken';
import verifyToken from '../middleware/verifyToken';
import { uIds } from './testdata/userTestData';
describe('verifyToken tests', () => {
const { uid1 } = uIds;
it('Should pass the userId to the request object if token is verified', () => {
const res = {};
const req = {
header: jest.fn(() => 'myAuthToken'),
};
const next = jest.fn();
const verify = jest
.spyOn(jwt, 'verify')
.mockReturnValueOnce({ userId: String(uid1) });
verifyToken(req, res, next);
expect(req.header).toHaveBeenCalledWith('x_auth-token');
expect(req.user).toEqual({ userId: String(uid1) });
expect(next).toHaveBeenCalled();
});
it('Should deny access if token is not present in header', () => {
const res = {
json(msg) {
expect(msg).toEqual({ message: 'Access denied' });
},
status(responseStatus) {
expect(responseStatus).toEqual(401);
return this;
},
};
const req = {
header: jest.fn(),
};
const next = jest.fn();
verifyToken(req, res, next);
expect(req.header).toHaveBeenCalledWith('x_auth-token');
expect(req.user).not.toEqual({ userId: String(uid1) });
});
it('Should deny access if token is invalid', () => {
const res = {
send(text) {
expect(text).toEqual('Invalid Token');
},
status(responseStatus) {
expect(responseStatus).toEqual(400);
return this;
},
};
const req = {
header: jest.fn(() => 123),
};
const next = jest.fn();
const verify = jest.fn();
verifyToken(req, res, next);
expect(req.header).toHaveBeenCalledWith('x_auth-token');
expect(req.user).not.toEqual({ userId: String(uid1) });
});
});
This passes the tests. However I'm not sure about the validity of the test.