jwt mock doens't get called

// auth.test.js
import mocha from 'mocha';
import sinon from 'sinon';
import { expect } from 'chai';
import client from 'socket.io-client';
import jwt from 'json-web-token';
import '../index.js';

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

describe.only('Connection', () => {
    it('should connect to the socket server', (done) => {
        const authStub = sinon.stub(jwt, 'decode').callsFake((secret, payload, callback) => {
            console.log('secret', secret);
            console.log('payload', payload);
            console.log('callback', callback);
            return callback(null, {data: 'someuser'});
        });

        const connection = new client(`http://localhost:${process.env.PORT}`);

        expect(authStub.called).to.be.true();
        expect(connection.connected).to.be.true();

        connection.on('message', (data) => {
            expect(typeof data).to.be.equals('string');
            done();
        });
    });
});


// lib/auth.js

import jwt from 'json-web-token';

const secret = 'some secret key, prefer .pem files';

const decode = (payload) => jwt.decode(secret, payload, (err, data) => {
    return !err ? data : err;
});

const auth = (headers, socket) => {
    let authorization;

    if (headers.authorization !== undefined) {
        authorization = headers.authorization;
    } else {
        authorization = null;
    }

    if (!(decode(authorization) instanceof Error)) {
        socket.emit('message', 'client connected');
        return true;
    } else {
        socket.emit('message', 'client unauthorized');
        return false;
    }
};

export default auth;