FLUTTER TESTING STRATEGIES

// Mocking with Mockito
import 'package:mockito/mockito.dart';
import 'package:mockito/annotations.dart';

@GenerateMocks([ApiService, DatabaseService])
import 'test_file.mocks.dart';

class UserRepository {
  final ApiService apiService;
  final DatabaseService dbService;
  
  UserRepository(this.apiService, this.dbService);
  
  Future<User> getUser(String id) async {
    try {
      final user = await apiService.fetchUser(id);
      await dbService.saveUser(user);
      return user;
    } catch (e) {
      return await dbService.getUser(id);
    }
  }
}

// Test with mocks
void main() {
  group('UserRepository', () {
    late MockApiService mockApiService;
    late MockDatabaseService mockDbService;
    late UserRepository userRepository;
    
    setUp(() {
      mockApiService = MockApiService();
      mockDbService = MockDatabaseService();
      userRepository = UserRepository(mockApiService, mockDbService);
    });
    
    test('should return user from API and save to database', () async {
      // Arrange
      const userId = '123';
      final expectedUser = User(id: userId, name: 'John Doe');
      
      when(mockApiService.fetchUser(userId))
          .thenAnswer((_) async => expectedUser);
      when(mockDbService.saveUser(expectedUser))
          .thenAnswer((_) async => {});
      
      // Act
      final result = await userRepository.getUser(userId);
      
      // Assert
      expect(result, equals(expectedUser));
      verify(mockApiService.fetchUser(userId)).called(1);
      verify(mockDbService.saveUser(expectedUser)).called(1);
    });
    
    test('should fallback to database when API fails', () async {
      // Arrange
      const userId = '123';
      final expectedUser = User(id: userId, name: 'John Doe');
      
      when(mockApiService.fetchUser(userId))
          .thenThrow(Exception('Network error'));
      when(mockDbService.getUser(userId))
          .thenAnswer((_) async => expectedUser);
      
      // Act
      final result = await userRepository.getUser(userId);
      
      // Assert
      expect(result, equals(expectedUser));
      verify(mockApiService.fetchUser(userId)).called(1);
      verify(mockDbService.getUser(userId)).called(1);
      verifyNever(mockDbService.saveUser(any));
    });
  });
}

// Golden Tests for UI consistency
testWidgets('login screen golden test', (WidgetTester tester) async {
  await tester.pumpWidget(MaterialApp(home: LoginScreen()));
  await expectLater(
    find.byType(LoginScreen),
    matchesGoldenFile('golden/login_screen.png'),
  );
});

// Custom matchers
Matcher hasErrorMessage(String message) {
  return predicate<Widget>((widget) {
    if (widget is Text) {
      return widget.data == message && 
             widget.style?.color == Colors.red;
    }
    return false;
  }, 'has error message: $message');
}