firestore-offline-test.ts

import * as admin from 'firebase-admin'
import * as fft from 'firebase-functions-test'
const ft = fft()
import * as sinon from 'sinon'
import { makeUppercase, addMessage } from './function'

describe('order', () => {
  describe('makeUpperCase', () => {
    it('should upper case input and write it to /uppercase', async () => {
      const fakeSnaphost = ft.firestore.makeDocumentSnapshot({
        original: 'hoge'
      }, 'user/1') as FirebaseFirestore.DocumentSnapshot

      sinon.stub(fakeSnaphost.ref, 'set').returns(true)

      const wrapped = ft.wrap(makeUppercase)
      expect(await wrapped(fakeSnaphost)).toBe(true)
    })
  })

  describe('addMessage', () => {
    it('should return a 303 redirect', async () => {
      const collection = 'messages'
      const addParam = { original: 'input' }
      const firestoreStub = sinon.stub()
      const refStub = sinon.stub()
      const addStub = sinon.stub()

      sinon.stub(admin, 'firestore').get(() => firestoreStub)
      firestoreStub.returns({ collection: refStub })
      refStub.withArgs(collection).returns({ add: addStub })
      addStub.withArgs(addParam).returns(Promise.resolve({ ref: 'new_ref' }))

      const req = { query: { text: 'input' } } as any
      const res = {
        redirect: (code, url) => {
          expect(code).toBe(303)
          expect(url).toBe('new_ref')
        }
      } as any

      await addMessage(req, res)
    })
  })
})

function.ts

import * as admin from 'firebase-admin'
import * as functions from 'firebase-functions'

export const makeUppercase = functions.firestore.document('/messages/{documentId}')
  .onCreate((snap, context) => {
    const original = snap.data()!.original
    console.log('Uppercasing', context, original)
    const uppercase = original.toUpperCase()
    console.log(uppercase)
    return snap.ref.set({ uppercase }, { merge: true })
  })

export const addMessage = functions.https.onRequest((req, res) => {
  console.log(req)
  console.log(res)
  const original = req.query.text
  return admin.firestore().collection('messages').add({ original: original }).then((writeResult) => {
    return res.json({ result: `Message with ID: ${writeResult.id} added.` })
  })
})

Thank you, this has been incredibly helpful