React Native Firestore mock does not work with react-native-firebase package

[GitGeddes]

Description

I am using React Native with the react-native-firebase package and tried using firestore-jest-mock to mock my database. Currently, my tests fail when using the mock as the documentation suggests. The documentation for these two packages do not align.

The react-native-firestore package documentation suggests importing firestore as the default export like so and calling firestore as the default function:

import firestore from '@react-native-firebase/firestore';

const usersCollection = firestore().collection('users');

Whereas firestore-jest-mock documentation suggests importing an injected Firestore stub that does not exist in @react-native-firebase/firestore then calling its constructor.

// mockReactNativeFirestore called above
test('testing stuff', () => {
  const { Firestore } = require('@react-native-firebase/firestore'); // Doesn't normally exist in this package
  const firestore = new Firestore();

  // Notice we're not calling firestore as a function
  return firestore
    .collection('users')
    .get()
    .then(userDocs => {
      expect(mockCollection).toHaveBeenCalledWith('users');
      expect(userDocs.docs[0].data().name).toEqual('Homer Simpson');
    });
});

I am not familiar with the @google-cloud/firestore package and how the documentation suggests we use it, so I'm not sure how different it is from react-native-firebase. I utilize other parts of the API like FieldValue and FieldPath in my production code. When using mockReactNativeFirebase the code I wanted to test would fail to load, saying these were all undefined or that firestore is not a function.

Steps to reproduce

1. Create new React Native project
2. Install @react-native-firebase/firestore and firestore-jest-mock
3. Set up Jest and Firestore mock using firestore-jest-mock documentation
4. Create tests for firestore using @react-native-firebase/firestore documentation

firestore.test.ts

import {mockCollection} from 'firestore-jest-mock/mocks/firestore';
import firestore, {firebase} from '@react-native-firebase/firestore';

describe('firestore-jest-mock tests', () => {
  it('gets a user', async () => {
    await firestore().collection('users').doc('test').get();
    expect(mockCollection).toHaveBeenCalledWith('users');
  });
  it('creates and uses an increment function', async () => {
    const incrementFunction = firebase.firestore.FieldValue.increment(1);
    await firestore()
      .collection('users')
      .doc('test')
      .set({followerCount: incrementFunction}, {merge: true});
    expect(mockCollection).toHaveBeenCalledWith('users');
  });
});

firestoreMock.setup.ts

import {mockReactNativeFirestore} from 'firestore-jest-mock';

mockReactNativeFirestore({
  database: {
    users: [
      {
        id: 'test',
        followerCount: 0,
      },
    ],
  },
});

// Needed to get Jest working in a React Native project
jest.mock('react-native/Libraries/EventEmitter/NativeEventEmitter');

Expected result

Firestore tests pass.

Actual result

Tests fail after using mockReactNativeFirestore({ database: { ... }}).

When running Jest tests:

...
    TypeError: (0 , _firestore2.default) is not a function

      4 | describe('firestore-jest-mock tests', () => {
      5 |   it('gets a user', async () => {
    > 6 |     await firestore().collection('users').doc('test').get();
...
    TypeError: Cannot read properties of undefined (reading 'firestore')

       8 |   });
       9 |   it('creates and calls an increment function', async () => {
    > 10 |     const incrementFunction = firebase.firestore.FieldValue.increment(1);
...

The same errors appear when trying to render components that reference firestore() during tests as well.

Environment

• Node version: 20.11.1
• React Native version 0.74.3
• React version 18.2.0
• @react-native-firebase/app: "^20.1.0",
• @react-native-firebase/firestore: "^20.1.0",
• firestore-jest-mock: "^0.25.0"

Potential Fix

I have already created a patch using patch-package to fix these errors in my project:

patches/firestore-jest-mock+0.25.0.patch

diff --git a/node_modules/firestore-jest-mock/mocks/reactNativeFirebaseFirestore.js b/node_modules/firestore-jest-mock/mocks/reactNativeFirebaseFirestore.js
index 2f0e0ea..574b26a 100644
--- a/node_modules/firestore-jest-mock/mocks/reactNativeFirebaseFirestore.js
+++ b/node_modules/firestore-jest-mock/mocks/reactNativeFirebaseFirestore.js
@@ -25,7 +25,18 @@ const mockReactNativeFirestore = (overrides = {}, options = defaultOptions) => {
 function mockModuleIfFound(moduleName, overrides, options) {
     try {
         require.resolve(moduleName);
-        jest.doMock(moduleName, () => firestoreStub(overrides, options));
+        jest.doMock(moduleName, () => {
+            const stub = firestoreStub(overrides, options);
+            return {
+                __esModule: true,
+                default: () => new (stub.Firestore)(),
+                firebase: {
+                    firestore: {
+                        ...stub
+                    }
+                }
+            }
+        });
     }
     catch (e) {
         // eslint-disable-next-line no-console

Notice that instead of returning the firestoreStub directly, it now returns as an esModule with a default method so that we can use firestore() how @react-native-firebase/firestore suggests. I also added the firebase object so that it matches the exports of @react-native-firebase/firestore. For example, the suggested way to use FieldValue and FieldPath are like so:

import { firebase } from '@react-native-firebase/firestore`;

const incrementFunction = firebase.firestore.FieldValue.increment(1);
const fieldPath = new firebase.firestore.FieldPath('parent', 'child');

With my patch all of these tests pass now with no changes to my production code. I'd like to make this change a PR, as well as updating documentation and test cases. I looked at the tests and this would break every mockReactNativeFirestore test in full-setup-library-firestore.test.js but only require minor, repetitive changes. Forgive me if this is the wrong way to suggest this change.