Riverpodを使った単体テスト

auth_providers.dart

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';

// FirebaseAuthインスタンスのプロバイダ
final authProvider = Provider((ref) => FirebaseAuth.instance);

// AuthRepositoryのプロバイダ
final authRepositoryProvider =
    Provider<AuthRepository>((ref) => AuthRepository(ref.read));
    
class AuthRepository {
  // コンストラクタでReaderを受け取る
  AuthRepository(this._read);

  final Reader _read;

  // Readerを使った処理
  Stream<User?> get authStateChanges => _read(authProvider).authStateChanges();
}

auth_repository_test.dart

void main() {
  // AuthRepositoryで使うauthProviderの値をMockFirebaseAuthで上書き
  final container = ProviderContainer(
    overrides: [
      authProvider.overrideWithValue(
        MockFirebaseAuth(),
      ),
    ],
  );
  
  // MockFirebaseAuthで上書きされたauthProviderを含むReaderをコンストラクタに渡す
  final authRepo = AuthRepository(container.read);  
}

mock_firebase_auth.dart

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:mocktail/mocktail.dart';

class MockUser extends Mock implements User {}

final MockUser mockUser = MockUser();

class MockFirebaseAuth extends Mock implements FirebaseAuth {
  @override
  Stream<User> authStateChanges() {
    return Stream.fromIterable(
      [mockUser],
    );
  }  
}