开玩笑模拟 function 返回未定义而不是 object

Question

I'm trying to create unit tests for my auth middleware in an Express app.

The middleware is as simple as this:

const jwt = require('jsonwebtoken');

const auth = (req, res, next) => {
    const tokenHeader = req.headers.auth; 

    if (!tokenHeader) {
        return res.status(401).send({ error: 'No token provided.' });
    }

    try {
        const decoded = jwt.verify(tokenHeader, process.env.JWT_SECRET);

        if (decoded.id !== req.params.userId) {
            return res.status(403).json({ error: 'Token belongs to another user.' });
        }

        return next();
    } catch (err) {
        return res.status(401).json({ error: 'Invalid token.' });
    }
}

module.exports = auth; 

And this is my test, where I want to ensure that if the token is ok everything will go smoothly and the middleware just calls next() :

it('should call next when everything is ok', async () => {
        req.headers.auth = 'rgfh4hs6hfh54sg46';
        jest.mock('jsonwebtoken/verify', () => {
            return jest.fn(() => ({ id: 'rgfh4hs6hfh54sg46' }));
        });
        await auth(req, res, next);
        expect(next).toBeCalled();
});

But instead of returning the object with and id field as desired, the mock always returns undefined. I have tried returning the object instead of jest.fn() but it didn't work too.

I know there are some similar threads here on stack overflow but unfortunately none of the solutions proposed worked for me.

If more context is needed, here is my full test suite. Thanks in advance.

Answer 1

One way to solve this is to mock the jsonwebtoken module and then use mockReturnValue on the method to be mocked. Consider this example:

const jwt = require('jsonwebtoken');

jest.mock('jsonwebtoken');

jwt.verify.mockReturnValue({ id: 'rgfh4hs6hfh54sg46' });

it('should correctly mock jwt.verify', () => {
  expect(jwt.verify("some","token")).toStrictEqual({ id: 'rgfh4hs6hfh54sg46' })
});