Firestore instance in snapshot.ref go undefined after make a document query request to the database

[ndpdarshana]

Description

The QueryDocumentSnapshot passed to onCreate() trigger failed to retrieve FakeFirestore instance within its ref value after query a document from the database.

Steps to reproduce

1. Write a onCreate() functions trigger

   export const setupActionTrigger = () => {
     return functions.firestore.document('note/{id}').onCreate(async(snapshot) => {
       if(snapshot.exists){
         console.log(snapshot.ref);
         const userRef = await admin.firestore().doc(`users/123`}).get();
         console.log(snapshot.ref);
       }
     });
   }
   

2. Make a test class

 describe('actionTrigger', () => {
   const test = firebaseFunctionsTest(); 
   let actionTriggerFunction: WrappedFunction;
   
   beforeAll(() => {
     fakeFirestore = new FakeFirestore({
       note: [{id: '123', note: 'test note', uid: 'xyz'}],
       users: [{id:'xyz', username: 'xyzlmn'}]
     });
     mockFirebase({database: fakeFirestore.database});
     admin.initializeApp();
     
     const {setupActionTrigger} = require('../src/test-trigger');
     actionTriggerFn = test.wrap(setupActionTrigger());
   }

   asterAll(() => {
     jest.clearAllMocks();
     jest.resetAllMocks();
     test.cleanup();
   });

  it('should pass', async () => {
    const doc = await fakeFirestore.doc('note/123').get();
    await actionTrigger(doc);
  })
 }

3. Note that the first console.log in the trigger function for snapshot.ref print with FakeFirestore instance that provided by test suit.
4. Note that the second console.log in the trigger function print without FakeFirestore instance, instead it says firestore:undefined

Expected result

Firesore instance with provided FakeFirestore instance would remain untouched with snapshot object after retrieving a document from the database query as shown in the trigger function

Actual result

The snapshot object reference FakeFirestore object went undefined after making the database query

Environment

• Node version: 12.20.1

[ndpdarshana]

I've just found out that this happens when calling the admin.firestor() call on the functions class. Somehow, admin.firestor() call resets the already obtained snapshot inside the trigger function.