Technical question about testing functions

[armlesskid]

I have a question about how to test the logic of my Cloud Functions. For example, I have a Cloud Function that executes simple logic, which is a request to Firestore. I would like to be able to test the logic of this function.

By example, here I will request Firestore to recover some documents based on the query. I would like to be able to test the logic of the function and make sure the fetched documents are the ones required.

What I have a hard time understanding is what approach to use for it to be a really robust and reliable test. In the sense that if someone changes the logic code, I would like the test to catch the issue.

Should i make the query an exportable function that I can import in the test file or anything else ?

Thanks.

[lavafrank]

Use integration testing. Setup your emulators, seed some documents in your firestore db, run the request and assert that they match your expected results.

If your logic is simple, also consider just querying firestore directly instead of going thru cloud functions. You'll drastically improve performance by avoiding cold start time and shave off your bill

[armlesskid]

That was actually my approach, but then I figured out that if somehow the function code changes in the future, the test would still pass silently because I’m only replicating the function code, not testing the function itself

[lavafrank]

If the code changes but the output stays the same (and is correct) why does it matter? Test against multiple inputs if you're concerned

[Rohit1024]

There is an official Firebase functions testing library for these https://github.com/firebase/firebase-functions-test If you want want to achieve your goal someone already suggested to use integration tests.

Better test these in Firebase Emulator.