How to mock/intercept calls to mongoDB atlas during tests? (cloud DB) - node.js

Question

I have an express app (REST API) which connects to a mongoDB cluster on MongoDB Atlas (the cloud database) during tests. I'm using Mocha to test.
I have an end-to-end test (which uses the database) but for the majority of the tests I want to mock/stub the calls to the database so that it's isolated.
I've tried using nock to intercept the network connections and mock the response, but from what I can see nock is only for http calls and mongoDB Atlas uses DNS (starts with mongodb+srv:, see here for more info) and I think this is why I can't get this to work.
I've also trying to stub the Model. I'm struggling to get this working but it seems like it might be an option?
// The route
router.post('/test', async (req, res) => {
const { name } = req.body;
const example = new ExampleModel({ name: name})
// this should be mocked
await example.save();
res.status(200);
});
// The test
describe('POST /example', () => {
it('Creates an example', async () => {
// using supertest to make http call to my API app
const response = await request(app)
.post('/test')
.type("json")
.send({ 'name': 'test-name' })
// expect the model to have been created and then saved to the database
});
});
I'm expecting that when I run the test, it will make a POST to the API, which won't make a call to the database but will return fake data (as though it had).

Answer 1

I've found some really useful resources and sharing them:
Isolating mongoose unit tests (including model methods like findOne guide
Stubbing the save method on a model: Stubbing the mongoose save method on a model (I just used `sinon.stub(ExampleModel.prototype, 'save').
// example code
it('Returns 400 status code', async () => {
sinon.stub(ExampleModel, 'findOne').returns({ name: 'testName' });
const saveStub = sinon.stub(ExampleModel.prototype, 'save');
const example = new ExampleModel({ name: 'testName' })
const response = await request(app)
.post('/api/test')
.type("json")
.send({ name: 'testName' })
sinon.assert.calledWith(Hairdresser.findOne, {
name: 'testName'
});
sinon.assert.notCalled(saveStub)
assert.equal(response.res.statusCode, 400);
});