How to stub external services in Firebase emulator? - firebase

Question

I have one firestore trigger function that is creating DNS record based on the slug attribute. I have some unit tests where I am stubbing #google-cloud/dns module so no external HTTP request is made. However, I have several integration tests as well. Those are hitting local firebase emulator (localhost:8080).
For instance, whilst testing firestore rules, I am simply calling db.collection('path').add(model) and that is triggering callable function inside emulator process.
Tests are running by this command: firebase emulators:exec 'mocha --config spec/.mocharc.yml
At first, it is initializing emulators and then running tests. As far as I understood these are different processes. So inside the mocha process, I am able to stub, mock with modules. On the other hand, inside the emulator process, functions, modules, dependencies are already loaded as it is. So when I am running this test script for testing firestore rules inside mocha test suite:
await assertSucceeds(db.doc('stores').set(store));
It actually runs the handler and sends the request to the google cloud DNS. Did anyone face issues something like this? Thanks in advance.

Answer 1

I'm facing the same situation. My plan is to make the Cloud Function initialize itself with a stubbed service that will record its own calls to a log collection in Firestore when NODE_ENV=test. Then the test will check whether the call was recorded by querying that collection.
test('fanOutCategoryFields', async () => {
// Initialize Firebase and seed test data
const app = await setup({
'categories/1': {
name: 'Some Name',
},
'posts/1': {
categoryId: '1',
},
})
// Update a document (will trigger the Cloud Function)
await app
.firestore()
.collection('categories')
.doc('1')
.update({ name: 'New Name' })
// Wait for the Cloud Function to run
await new Promise(resolve => setTimeout(resolve, 3000))
// Query the collection where function calls are recorded
const calls = await app
.firestore()
.collection('_calls')
.get()
.then(snap => snap.docs.map(snap => snap.data()))
// Check if Algolia was called with the expected arguments
expect(calls).toEqual([
{
fn: 'algolia.update',
args: ['products', '1', { categoryName: 'New Name' }],
},
])
})