How to mock the FirebaseApp in flutter

Question

I am trying to test a method that uses FirebaseFirestore but I am not able to mock the FirebaseFirestore.instance property.

I am following these examples:

1. Initializing the core: https://firebase.flutter.dev/docs/overview#initializing-flutterfire
2. Using the firestore plugin: https://firebase.flutter.dev/docs/firestore/usage

I am using the code below for my class and it is working well, which means the firestoreInstance is loaded correctly

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';

void main() {
  WidgetsFlutterBinding.ensureInitialized();
  runApp(
    Main(firebaseApp: Firebase.initializeApp()),
  );
}

class Main extends StatelessWidget {
  final Future<FirebaseApp> firebaseApp;
  const Main({this.firebaseApp});

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: firebaseApp,
      builder: (context, snapshot) {
        if (snapshot.connectionState == ConnectionState.done) {
          final firestoreInstance = FirebaseFirestore.instanceFor(
            app: snapshot.data,
          );
          return MyWidget();
        }
        return CircularProgressIndicator();
      },
    );
  }
}

But when I run the test below I got the message:

"The following FirebaseException was thrown building Builder(dirty): [core/no-app] No Firebase App '[DEFAULT]' has been created - call Firebase.initializeApp()"

import 'package:firebase_core/firebase_core.dart';
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mockito/mockito.dart';

class MockFirebaseApp extends Mock implements FirebaseApp {}

void main() {
  FirebaseApp firebaseApp;

  setUp(() async {
    TestWidgetsFlutterBinding.ensureInitialized();
    firebaseApp = MockFirebaseApp();
  });

  group('Main', () {
    testWidgets('Loads my widget', (WidgetTester tester) async {
      await tester.runAsync(() async {
        await tester.pumpWidget(
          Main(firebaseApp: Future.value(firebaseApp)),
        );

        expect(find.byType(CircularProgressIndicator), findsOneWidget);
      });
    });
  });
}

Answer 1

I had the same problem. Using this answer I found the solution.

1. Copy the contents of: https://github.com/FirebaseExtended/flutterfire/blob/master/packages/firebase_auth/firebase_auth/test/mock.dart into a file, that you can import into your tests, where you need to initialize a Firebase app.

2. Call setupFirebaseAuthMocks(); at the top of your main function for all your tests.

3. In your setUpAll function, call await Firebase.initializeApp(); (You can also put this in your main function under setupFirebaseAuthMocks(); will still work).

Now you should have a mocked Firebase app.

Here is a full example:

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:flutter_test/flutter_test.dart';
import '../lib/authentication/your_auth_using_firebase.dart';
import './mock.dart'; // from: https://github.com/FirebaseExtended/flutterfire/blob/master/packages/firebase_auth/firebase_auth/test/mock.dart



void main() {
  // TestWidgetsFlutterBinding.ensureInitialized(); Gets called in setupFirebaseAuthMocks()
  setupFirebaseAuthMocks();

  setUpAll(() async {
    await Firebase.initializeApp();
  });

  testWidgets('Your Test', (WidgetTester tester) async {
    final YourFirebaseAuthClass authService = YourFirebaseAuthClass();
    // Tests to write
  });
}

Answer 2

Maybe the cloud_firestore_mocks package is useful for you:

Fakes to write unit tests for Cloud Firestore. Instantiate a MockFirestoreInstance, then pass it around your project as if it were a FirestoreInstance. This fake acts like Firestore except it will only keep the state in memory. To help debug, you can use MockFirestoreInstance.dump() to see what's in the fake database. This is useful to set up the state of your database, then check that your UI behaves the way you expect.

Example from the docs:

import 'package:cloud_firestore_mocks/cloud_firestore_mocks.dart';

void main() {
  final instance = MockFirestoreInstance();
  await instance.collection('users').add({
    'username': 'Bob',
  });
  final snapshot = await instance.collection('users').get();
  print(snapshot.documents.length); // 1
  print(snapshot.documents.first['username']); // 'Bob'
  print(instance.dump());
}