Returned an undefined when resolving JWTVerifyStub- Mocha/Chai

Question

I'm working on creating test scripts for my validateAuth function, but I've encountered an issue where I'm getting an undefined value from this line of code const {_id} = jwt.verify(token, process.env.SECRET);. Instead of the expected value "fakeUserId," I'm seeing {_id: undefined} when I log it. Can someone please help me identify where I might be making a mistake?

Test Script:

const expect = chai.expect;
const sinon = require('sinon');
const validateAuth = require('../middleware/validateAuth');
const User = require('../models/userModel');
const jwt = require('jsonwebtoken');

process.env.SECRET = 'your_test_secret';

describe('validate authentication', () => {
  let req, res, next, jwtVerifyStub, findOneStub;
  const mockUserDocument = { _id: 'fakeUserId' };

  beforeEach(() => {
    jwtVerifyStub = sinon.stub(jwt, 'verify')
    findOneStub = sinon.stub(User, 'findOne').resolves(mockUserDocument);
    next = sinon.spy();
    req = {
      headers: {
        authorization: 'Bearer fakeEncryptedToken'
      }
    }
    res = {
      status: sinon.stub(),
      json: sinon.stub()
    }
    res.status.returns(res)
  })
  afterEach(() => {
    sinon.restore();
  })
  it('successfully validates authorized user', async () => {
    jwtVerifyStub.withArgs('fakeEncryptedToken', 'your_test_secret').resolves({_id: 'fakeUserId'})

    await validateAuth(req, res, next);
    
    expect(next.calledOnce).to.be.true
  })
})

validateAuth.js

const jwt = require('jsonwebtoken');
const User = require('../models/userModel');

const validateAuth = async (req, res, next) => {
  const { authorization } = req.headers;

  if (!authorization) {
    return res.status(401).json({error: 'require authorization token'});
  };

  const token = authorization.split(' ')[1];
  try {
    const {_id} = jwt.verify(token, process.env.SECRET);

    req.user = await User.findOne({_id}).select('_id');
    next();
  }
  catch(err) {
    res.status(401).json({error: 'request is not authorized'})
  }
}

module.exports = validateAuth;