Flutter Testing

Testing patterns for Flutter apps with BLoC/Cubit, Clean Architecture, bloc_test, and mocktail.

When to Use

•Writing BLoC/Cubit, widget, or integration tests
•Mocking dependencies with mocktail
•Testing Clean Architecture layers
•Setting up test coverage or TDD workflow

Test Types

Type	Purpose	Coverage
Unit	BLoC/Cubit, repositories	80%+
Widget	UI components	Key flows
Integration	E2E flows	Critical paths

Dependencies

yaml

dev_dependencies:
  flutter_test:
    sdk: flutter
  bloc_test: ^9.1.0
  mocktail: ^1.0.0
  integration_test:
    sdk: flutter

BLoC/Cubit Testing

dart

import 'package:bloc_test/bloc_test.dart';
import 'package:mocktail/mocktail.dart';

class MockRepository extends Mock implements FeatureRepository {}

blocTest<FeatureCubit, FeatureState>(
  'emits [loading, loaded] on success',
  build: () {
    when(() => mockRepo.getData(any()))
        .thenAnswer((_) => TaskEither.right(mockData));
    return FeatureCubit(mockRepo);
  },
  act: (cubit) => cubit.loadData('id'),
  expect: () => [
    const FeatureState(status: Status.loading),
    FeatureState(status: Status.loaded, data: mockData),
  ],
  verify: (_) => verify(() => mockRepo.getData('id')).called(1),
);

Details: BLOC_CUBIT_TESTING.md

Widget Testing

dart

import 'package:flutter_test/flutter_test.dart';
import 'package:mocktail/mocktail.dart';

class MockFeatureCubit extends Mock implements FeatureCubit {}

testWidgets('displays data when loaded', (tester) async {
  final mockCubit = MockFeatureCubit();
  when(() => mockCubit.state).thenReturn(
    FeatureState(status: Status.loaded, data: mockData),
  );

  await tester.pumpWidget(
    MaterialApp(
      home: BlocProvider(create: (_) => mockCubit, child: FeaturePage()),
    ),
  );

  expect(find.text('Expected Data'), findsOneWidget);
});

testWidgets('handles tap', (tester) async {
  await tester.tap(find.byKey(Key('button')));
  await tester.pumpAndSettle();
  verify(() => mockCubit.loadData()).called(1);
});

Details: WIDGET_TESTING.md

Integration Testing

dart

import 'package:integration_test/integration_test.dart';

void main() {
  IntegrationTestWidgetsFlutterBinding.ensureInitialized();

  testWidgets('complete user journey', (tester) async {
    await tester.pumpWidget(MyApp());
    await tester.pumpAndSettle();

    await tester.tap(find.byKey(Key('nav_button')));
    await tester.pumpAndSettle();

    expect(find.text('Success'), findsOneWidget);
  });
}

Best Practices

✅ Test behavior not implementation • Mock dependencies only • Cover success AND failure • Use descriptive names • Test state transitions • Use verify() for interactions • Add keys to widgets • Use pumpAndSettle() after async

❌ Don't test private methods • Don't mock the thing being tested • Don't skip error tests • Don't use hard-coded delays

Commands

bash

flutter test                    # All tests
flutter test --coverage         # With coverage
flutter test test/path/         # Specific path
flutter test integration_test/  # Integration tests

Mocking Essentials

dart

// Setup
class MockRepo extends Mock implements FeatureRepo {}
when(() => mock.method(any())).thenAnswer((_) => TaskEither.right(data));

// Verify
verify(() => mock.method('arg')).called(1);
verifyNever(() => mock.method(any()));

// Fallback for custom types
setUpAll(() => registerFallbackValue(FakeFeature()));

References

•BLoC/Cubit Testing - State management patterns
•Widget Testing - UI testing and finders
•Mocking Patterns - Mocktail techniques
•Repository Testing - Testing repositories and datasources
•Integration Testing - E2E flows and user journeys
•Clean Architecture - Layer-by-layer testing strategy
•Advanced Patterns - Golden tests, performance, custom matchers

Quick Tips

•Use keys for reliable widget finding
•pumpAndSettle() after async operations
•Mock dependencies, not the thing being tested
•Test both success and failure paths
•Use isA<T>().having() for complex assertions