Library / FLUTTER-TESTING
flutter dart
npx skills add dhruvanbhalara/skills --skill flutter-testing

Testing Strategy

  • Test Pyramid: More unit and widget tests, fewer integration tests. Unit tests are fastest and cheapest.
  • Mirror Test Rule: 100% logic and widget coverage. No code without a test.
  • Mirror Organization: Test files MUST strictly mirror the lib/ directory structure and end with _test.dart.
  • Coverage Targets: Target 100% logic coverage for domain and bloc layers.
  • Test Independence: Each test MUST be independent. No shared mutable state between tests.

Unit Testing

  • Follow the Arrange-Act-Assert (Given-When-Then) convention for clear and maintainable tests
  • Use mocks for dependencies except for lightweight third-party services
  • Test business logic in isolation from the UI
  • For tests, ensure to create 5 to 8 tests for logical operations with real scenarios
  • Mocking Protocol: Use mocktail for all dependency mocking. STRICTLY prohibit using real implementation dependencies in unit tests.
  • Pure Logic: Business logic inside BLoCs or UseCases should be extracted to static pure functions for 100% unit test coverage.

Widget Testing

  • Write widget tests for all major UI components
  • Test user interactions and state changes
  • Widget Keys: Use Key('feature_action_id') format on interactive widgets for test access
  • Test Localization: Use AppLocalizations (context.l10n) in widget tests — no hardcoded strings

Integration Testing

  • Use IntegrationTestWidgetsFlutterBinding.ensureInitialized() at the start of integration tests
  • Interact with widgets via Key (e.g., find.byKey(const ValueKey('increment')))
  • Use pumpAndSettle() to wait for animations and async operations to complete
  • Run with: flutter test integration_test/

Test Naming & Structure

  • Test Naming: Use string interpolation for test group names: group('$ClassName', not group('ClassName',. This ensures consistency and enables better tooling support.
  • Test Grouping: Use group() to organize tests by feature, class, or state for clearer reporting.
  • Descriptive Names: Test names should clearly describe what is being tested and why.

Common Test Errors

  • A RenderFlex overflowed... — Wrap widget in Expanded or constrain dimensions in test
  • Vertical viewport was given unbounded height — Wrap ListView in SizedBox with fixed height in test
  • setState called during build — Defer state changes to post-frame callback

Running Tests

  • flutter test — Run all unit and widget tests
  • flutter test test/path/to/file_test.dart — Run specific test file
  • flutter test integration_test/ — Run integration tests
  • flutter test --coverage — Run with coverage report