TypeError: firebase.analytics is not a function when mocking with jest

Question

I am starting to use Jest for testing my React app, I am writing a basic test and I have an exception. The test code is the following

// __test__/App.test.js
import '@babel/polyfill'
import React from 'react';
import App from '../components/App'
import { render } from '@testing-library/react';

jest.mock('firebase/app')
// The error is the same with or without the following line:
firebase.analytics.mockResolvedValue(null)

it("renders without crashing", () => {
  render(<App />);
});

But when I run npx jest I get this output:

 FAIL  src/__test__/App.test.js
  ● Test suite failed to run

    TypeError: firebase.analytics is not a function

       8 | // Initialize Firebase
       9 | firebase.initializeApp(firebaseConfig);
    > 10 | firebase.analytics();
         |          ^
      11 | 
      12 | const db = firebase.firestore();
      13 | 

The app works as it should outside tests.

How can I do to propperly mock firebase to simply test than App renders without errors?

Answer 1

If someone is interested: I found the way to do this. I am mocking the functions I am using:

// __mocks__/firebase/app.js

module.exports = (function () {
  const _tareas = { ...initialData }
  return {
    initializeApp: () => null,
    analytics: () => null,
    firestore: () => ({
      collection: () => ({
        get: () => ({
          docs: _tareas.list.map(index => ({
            data: () => _tareas.byId[index],
            id: index,
          }))
        }),
        add: (tarea) => {
          const newIndex = _tareas.list.length
          _tareas.list.push(newIndex)
          _tareas.byId[newIndex] = tarea
        },
      })
    }),
  }
})()

I also had to create blank files __mocks__/firebase/analytics and __mocks__/firebase/firestore

I am going to implement the functions as I am needing them

Now it works as I expect