How to test nested firestore batch functions in redux saga using jest? - firebase

Question

In a react project I have a redux-saga file which I create and save new items on firebase backend(firestore).
In that saga function, I am getting a new write batch object first, then I update the firestore document, and finally I commit the batch.
Saga Worker
import { call, put } from 'redux-saga/effects'
import { db } from './firebase' // db: firebase.firestore()
export function* mySaga(item) {
try {
// init firestore batch.
const batch = yield call(db, db.batch)
// Set firestore document and save new item.
const itemRef = yield call ([db, db.doc], `/items/${item.id}`)
yield call([batch, batch.set], itemRef , item)
// Commit the batch.
yield call([batch, batch.commit])
yield put({type: 'success'})
} catch (err) {
yield put({type: 'error', payload: err})
}
}
Saga Worker's Test
import * as sagas from './mySaga'
describe('mySaga', () => {
const spyOnDoc = jest.spyOn(db, 'doc')
it('handles item creation', async () => {
const dispatched = []
await runSaga(
{ dispatch: action => dispatched.push(action) },
sagas.mySaga,
).toPromise()
expect(spyOnDoc).toHaveBeenCalledTimes(1)
// !!! Here I need to check for nested set and commit functions of the batch object created in saga.
})
})
How can I test the batch function's nested "set" and "commit" functions to check if they are called x times and called with proper inputs?
Any help would be appreciated.

Answer 1

After several attemps I figured out a way to accomplishing this kind of tests. In case if someone needs this solution, here it is.
db.batch() method creates a firebase.firestore.WriteBatch object. And this object has commit, set, update and delete methods. More details can be found here.
Final Saga Worker's Test
import * as sagas from './mySaga'
import { db } from './firebase' // db: firebase.firestore()
describe('mySaga', () => {
const spyOnDoc = jest.spyOn(db, 'doc')
// We are mocking the methods of this predefined object.
firestore.WriteBatch.set = jest.fn()
firestore.WriteBatch.commit = jest.fn()
// Then we implement those created mocks into the batch's mock implementation.
const spyOnBatch = jest.spyOn(db, 'batch').mockImplementation(() => ({
set: firestore.WriteBatch.set,
commit: firestore.WriteBatch.commit,
}))
it('handles item creation', async () => {
const dispatched = []
await runSaga(
{ dispatch: action => dispatched.push(action) },
sagas.mySaga,
{id: 123} // Item
).toPromise()
expect(spyOnDoc).toHaveBeenCalledTimes(1)
// Finally, we can test those nested object functions as below.
expect(firestore.WriteBatch.commit).toHaveBeenCalledTimes(1)
expect(firestore.WriteBatch.set).toHaveBeenCalledTimes(1)
expect(firestore.WriteBatch.set).toHaveBeenCalledWith(db.doc('/items/123'), {id: 123})
})
})