flutter-testing

Flutter Testing

Write and maintain Flutter tests at the right level: unit tests for business logic, widget tests for screens and components, integration tests for critical flows, and golden tests for visual regression.

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Test Pyramid

        [Integration Tests]  — critical end-to-end flows; device/emulator required; CI on merge only
          [Widget Tests]  — screens, components, interactions; run every commit
            [Unit Tests]  — business logic, providers, cubits, utilities; run every commit

Target distribution: 70%+ unit | 20–25% widget | 5–10% integration.

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Setup

dev_dependencies:
  flutter_test:
    sdk: flutter
  mocktail: ^1.0.0
  bloc_test: ^9.1.0
  network_image_mock: ^2.1.0

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Unit Tests

What to test: use cases, repository impls, Riverpod notifiers, Cubit/Bloc, validators, parsers, mappers, utilities.

Do NOT test: *.g.dart / *.freezed.dart, simple value objects with no logic, framework widgets (Text, Container), layout-only build methods.

Structure:

void main() {
  late MockProductRepository mockRepository;
  late GetProducts useCase;

  setUp(() {
    mockRepository = MockProductRepository();
    useCase = GetProducts(mockRepository);
  });

  group('GetProducts', () {
    test('returns list on success', () async {
      when(() => mockRepository.getProducts()).thenAnswer((_) async => fakeProducts);
      expect(await useCase.execute(), equals(fakeProducts));
    });
    test('propagates exception', () {
      when(() => mockRepository.getProducts()).thenThrow(const NetworkException('No connection'));
      expect(useCase.execute(), throwsA(isA<NetworkException>()));
    });
  });
}

Riverpod notifier tests: use ProviderContainer with overrideWithValue. Always call addTearDown(container.dispose).

Bloc/Cubit tests: use bloc_test blocTest<Cubit, State>() with build, act, expect, and optional verify.

See @references/state-management-snippets.md for full Riverpod and bloc_test examples.

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Widget Tests

Minimum per screen: test all four states — loading, success, error, empty.

Also test: user interactions (tap, scroll, form input), navigation triggers, complex reusable components.

Riverpod widget test:

testWidgets('shows product list on success', (tester) async {
  await tester.pumpWidget(
    ProviderScope(
      overrides: [productsNotifierProvider.overrideWith(() => FakeProductsNotifier())],
      child: const MaterialApp(home: ProductsScreen()),
    ),
  );
  await tester.pumpAndSettle();
  expect(find.text(fakeProducts.first.name), findsOneWidget);
});

For loading state: use tester.pump() (one frame), NOT pumpAndSettle — the latter waits until animation completes and may wait forever.

Bloc widget test: wrap with BlocProvider<Cubit>.value(value: mockCubit) and use whenListen from bloc_test.

Finder priority (most to least stable):

1. find.byKey(const Key('widget-id')) — survives text changes
2. find.byType(MyWidget) — stable for design system components
3. find.text('Submit') — fragile if copy changes

Always add Key to dynamically generated list items:

ListView.builder(
  itemBuilder: (context, i) => ProductTile(key: ValueKey(products[i].id), product: products[i]),
)

---

Integration Tests

// integration_test/app_test.dart
void main() {
  IntegrationTestWidgetsFlutterBinding.ensureInitialized();
  testWidgets('sign in and navigate to home', (tester) async {
    await tester.pumpWidget(const MyApp());
    await tester.pumpAndSettle();
    await tester.enterText(find.byKey(const Key('email-field')), 'test@example.com');
    await tester.tap(find.byKey(const Key('sign-in-button')));
    await tester.pumpAndSettle(const Duration(seconds: 5));
    expect(find.byType(HomeScreen), findsOneWidget);
  });
}

Rules:

• Use a dedicated test environment (staging Firebase / mock backend).
• Keep count small — integration tests are 10–100x slower than widget tests.
• Test only critical paths that widget tests cannot cover.
• Run in CI on merge to main only.

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Golden Tests

Catch unintended visual regressions in design system components and critical screens.

testWidgets('PrimaryButton matches golden — default', (tester) async {
  await tester.pumpWidget(/* MaterialApp > Scaffold > Center > PrimaryButton */);
  await expectLater(find.byType(PrimaryButton), matchesGoldenFile('goldens/primary_button_default.png'));
});

Update after intentional design changes: flutter test --update-goldens

Test at multiple device sizes by setting tester.view.physicalSize before pumping. Cover: all design system components, critical screens at phone/tablet breakpoints, dark vs. light mode.

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CI Commands

flutter test                            # unit + widget
flutter test --coverage                 # with coverage
genhtml coverage/lcov.info -o coverage/html
flutter test integration_test/ -d <device>
flutter test --update-goldens
flutter test --name "pattern"           # filter by test name

Coverage targets:

• Domain (use cases, entities): 90%+
• Data (repositories, datasources): 80%+
• Presentation (notifiers, cubits): 80%+
• UI widgets: covered by widget tests, not line coverage

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Cross-references

• Code examples: @references/state-management-snippets.md (Riverpod + Bloc test patterns)
• Agent: flutter-test-engineer
• Error types: @references/dart-error-mapping.md