Nodejs/Mocha - FieldValue.increment - FirebaseError: Function DocumentReference.update() called with invalid data - node.js

Question

I have the following code:
NOTE getDb() is wrapper around admin.firestore() see the link in the end of the question for more details.
let wordRef = await getDb().
.collection(DOC_HAS_WORD_COUNT)
.doc(word)
await wordRef.set({ word: word, 'count': 0 })
await wordRef.update('count', admin.firestore.FieldValue.increment(1))
When I execute it I get
FirebaseError: Function DocumentReference.update() called with invalid data. Unsupported field value: a custom object (found in field count)
How do I increment the value in node js, firestore, cloud functions?
NOTE: this problem is specific to Mocha testing, I didn't check but it will probably not fail on real env.
The problem is caused by the code using the real implementation in test, which need to be override by an emulator implementation, as explain in:
https://claritydev.net/blog/testing-firestore-locally-with-firebase-emulators/
Where u can also find the definition of getDb() I used in the code snipet

Answer 1

The following code will replace the firebase admin at run time, only when running in test env.
NOTE: this code is based on https://claritydev.net/blog/testing-firestore-locally-with-firebase-emulators/
and for a full solution, one need to do the same trick for db as explained in the link
//db.js
const admin = require("firebase-admin");
let firebase;
if (process.env.NODE_ENV !== "test") {
firebase = admin
}
exports.getFirebase = () => {
return firebase;
};
exports.setFirebase = (fb) => {
firebase = fb;
};
test:
// package.test.js
process.env.NODE_ENV = "test"
beforeEach(() => {
// Set the emulator firebase before each test
setFirebase(firebase)
});
import:
// package.test.js and package.js (at the top)
const { setFirebase } = require("../db.js")
code:
// package.js
let wordRef = await getDb()
.collection(DOC_HAS_WORD_COUNT)
.doc(word)
await wordRef.set({ word: word, 'count': 0 })
await wordRef.update('count', getFirebase().firestore.FieldValue.increment(1))