How to mock firestore query with mocha and sinon?

Question

W.r.t. How to mock firestore with mocha how do I mock the following firestore query using sinon?

import * as admin from "firebase-admin";
const db: FirebaseFirestore.Firestore = admin.firestore();
const storeSnapshot: = await db
        .doc(`/Client/${clientId}/Store/${storeId}`)
        .get();

I tried:

import * as _sinon from 'sinon';

it('Query Client collection not empty test', async () => {

const clientStoreDocStub = _sinon.stub(db, "doc");
clientStoreDocStub.withArgs("/Client/123/Store/789").resolves({
            id: "789",
            settings: [ {setting1: "Setting1-value", setting2: "Setting2-value"}, {setting1: "Setting3-value", setting2: "Setting4-value"}]
        });
clientStoreDocStub.withArgs("/Client/456/Store/012").resolves({
            id: "012",
            settings: [ {setting1: "Setting5-value", setting2: "Setting6-value"}, {setting1: "Setting7-value", setting2: "Setting8-value"}]
        });        
const storeSnapshot: FirebaseFirestore.DocumentSnapshot = await db
              .doc("/Client/123/Store/789")
              .get();
const store = storeSnapshot.data();
});

but get the following error:

  1) Mock firebase firestore Tests
       Query Client collection not empty test:
     TypeError: dbInit_1.db.doc(...).get is not a function

Answer 1

import * as _chai from "chai";
import * as chaiAsPromised from "chai-as-promised";
import * as admin from "firebase-admin";
import * as _sinon from 'sinon';
_chai.use(chaiAsPromised);
var expect = _chai.expect;
const db: FirebaseFirestore.Firestore = admin.firestore();

describe("Test with mock firestore", () => {
    var docRefStub;
    beforeEach(() => { docRefStub = _sinon.stub(db, "doc");});
    afterEach(() => {db.doc.restore();});
    it("Test should pass with valid request params", async () => {
        const expectedString = "Hello World!!!";
        const testCollection = {
            "/Client/123/Store/789": {
                 data: 1,
                 moreData: "Hello World!!!"
            }
        }
        const setSpy = _sinon.spy();
        docRefStub.callsFake(fakeFsDoc(testCollection, setSpy));
        await callAFunction("123", "789");
        expect(setSpy.called).to.be.true;
        expect(setSpy.getCall(0).args[0].data).to.not.be.null;
        expect(setSpy.getCall(0).args[0].moreData).to.deep.equal(expectedString);
    }
});

export function fakeFsDoc(database, setSpy = null) {
    return docId => {
        const data = database[docId] ?? undefined;
        return {
            get: async () => ({
               data: () => data
            }),
            set: setSpy
        }
    }
}