Jest integration test Express REST API with Mongoose - express

Question

everybody. I'm new to unit/integration testing and I'm having trouble with testing one of my API routes which involves file system operations and Mongoose model method calls. I need to be able mock mongoose model method as well as router's post method. Let me share you my router's post method.
documents.js
const { User } = require('../models/user');
const { Document } = require('../models/document');
const isValidObjectId = require('./../helpers/isValidObjectId');
const createError = require('./../helpers/createError');
const path = require('path');
const fs = require('fs');
const auth = require('./../middlewares/auth');
const uploadFile = require('./../middlewares/uploadFile');
const express = require('express');
const router = express.Router();
.
.
.
router.post('/mine', [auth, uploadFile], async (req, res) => {
const user = await User.findById(req.user._id);
user.leftDiskSpace(function(err, leftSpace) {
if(err) {
return res.status(400).send(createError(err.message, 400));
} else {
if(leftSpace < 0) {
fs.access(req.file.path, (err) => {
if(err) {
res.status(403).send(createError('Your plan\'s disk space is exceeded.', 403));
} else {
fs.unlink(req.file.path, (err) => {
if(err) res.status(500).send('Silinmek istenen doküman diskten silinemedi.');
else res.status(403).send(createError('Your plan\'s disk space is exceeded.', 403));
});
}
});
} else {
let document = new Document({
filename: req.file.filename,
path: `/uploads/${req.user.username}/${req.file.filename}`,
size: req.file.size
});
document.save()
.then((savedDocument) => {
user.documents.push(savedDocument._id);
user.save()
.then(() => res.send(savedDocument));
});
}
}
});
});
.
.
.
module.exports = router;
documents.test.js
const request = require('supertest');
const { Document } = require('../../../models/document');
const { User } = require('../../../models/user');
const mongoose = require('mongoose');
const fs = require('fs');
const path = require('path');
const config = require('config');
let server;
describe('/api/documents', () => {
beforeEach(() => { server = require('../../../bin/www'); });
afterEach(async () => {
let pathToTestFolder = path.join(process.cwd(), config.get('diskStorage.destination'), 'user');
await fs.promises.access(pathToTestFolder)
.then(() => fs.promises.rm(pathToTestFolder, { recursive: true }))
.catch((err) => { return; });
await User.deleteMany({});
await Document.deleteMany({});
server.close();
});
.
.
.
describe('POST /mine', () => {
let user;
let token;
let file;
const exec = async () => {
return await request(server)
.post('/api/documents/mine')
.set('x-auth-token', token)
.attach('document', file);
}
beforeEach(async () => {
user = new User({
username: 'user',
password: '1234'
});
user = await user.save();
user.leftDiskSpace(function(err, size) { console.log(size); });
token = user.generateAuthToken();
file = path.join(process.cwd(), 'tests', 'integration', 'files', 'test.json');
});
.
.
.
it('should return 400 if an error occurs during calculation of authorized user\'s left disk space', async () => {
jest.mock('../../../routes/documents');
let documentsRouter = require('../../../routes/documents');
let mockReq = {};
let mockRes = {}
let mockPostRouter = jest.fn();
mockPostRouter.mockImplementation((path, callback) => {
if('path' === '/mine') callback(mockReq, mockRes);
});
documentsRouter.post = mockPostRouter;
let error = new Error('Something went wrong...');
const res = await exec();
console.log(res.body);
expect(res.status).toBe(400);
expect(res.body.error).toHaveProperty('message', 'Something went wrong...');
});
.
.
.
});
});
What I want to do is, I need to be able call a mock user.leftDiskSpace(function(err, leftSpace)) user model method inside router.post('/mine', ...) route handler. I need to be able to get inside the if and else brances by callback function of user.leftDiskSpace(). How can I do that?
Thanks in advance.