Flutter testing

Unit tests

Invoked by the flutter-knowledge skill (or directly via /flutter-testing) only when the user explicitly asks for tests — never generate test files as a side effect of scaffolding a feature.

Tooling: mocktail for mocks, bloc_test for cubit tests. Add both to dev_dependencies in pubspec.yaml if not already present.

Layout: tests mirror the lib/ feature tree under test/, one _test.dart per source file:

test/feature/<feature>/
  data/
    data_source/<feature>_remote_data_source_test.dart
    repository/<feature>_repository_test.dart
  presentation/
    <screen>_screen/logic/<screen>_cubit_test.dart

Mocktail mocks: declare class MockX extends Mock implements X {} per collaborator, at the top of the test file. Register a fallback value in setUpAll before using any() for any non-primitive argument type — mocktail throws otherwise.

Data source tests: mock ApiConsumer, stub its get/post/etc. call, and assert the returned model is parsed correctly and that params were passed through .toJson() as the request body/query.

Repository tests: mock the abstract data source and NetworkStatus. Group by method (matching the cubit's per-method state naming), covering three branches: offline → Result.failure(ServerFailure.noNetwork()) without calling the data source; data source succeeds → Result.success(...); data source throws a Failure → Result.failure(error).

class MockXRemoteDataSource extends Mock implements XRemoteDataSource {}
class MockNetworkStatus extends Mock implements NetworkStatus {}

void main() {
  late XRepositoryImp repository;
  late MockXRemoteDataSource dataSource;
  late MockNetworkStatus networkStatus;

  setUp(() {
    dataSource = MockXRemoteDataSource();
    networkStatus = MockNetworkStatus();
    repository = XRepositoryImp(dataSource, networkStatus);
  });

  group('getX', () {
    test('returns failure without calling the data source when offline', () async {
      when(() => networkStatus.isConnected).thenAnswer((_) async => false);

      final result = await repository.getX();

      expect(result, Result.failure(ServerFailure.noNetwork()));
      verifyNever(() => dataSource.getX());
    });

    test('returns success when the data source call succeeds', () async {
      when(() => networkStatus.isConnected).thenAnswer((_) async => true);
      when(() => dataSource.getX()).thenAnswer((_) async => GlobalResponse(data: XModel()));

      final result = await repository.getX();

      expect(result, isA<Success>());
    });
  });
}

Cubit tests: mock the repository, use blocTest per method. Because the cubit fires its initial fetch from the constructor, stub the repository's response before calling build: — blocTest subscribes to the stream as soon as build() returns, in time to catch the states that fetch emits.

class MockXRepository extends Mock implements XRepository {}

void main() {
  late MockXRepository repository;

  setUp(() => repository = MockXRepository());

  group('getX', () {
    blocTest<XCubit, XState>(
      'emits [GetXLoadingState, GetXSuccessState] when getX succeeds',
      setUp: () => when(() => repository.getX())
          .thenAnswer((_) async => Result.success(GlobalResponse(data: XModel()))),
      build: () => XCubit(repository),
      expect: () => [const GetXLoadingState(), const GetXSuccessState()],
    );

    blocTest<XCubit, XState>(
      'emits [GetXLoadingState, GetXFailureState] when getX fails',
      setUp: () => when(() => repository.getX())
          .thenAnswer((_) async => Result.failure(ServerFailure(message: 'error'))),
      build: () => XCubit(repository),
      expect: () => [const GetXLoadingState(), isA<GetXFailureState>()],
    );
  });
}

What NOT to do

• Do not write unit tests unprompted. Only add them when the user explicitly asks.
• Do not use mockito/@GenerateMocks or hand-rolled fakes for new tests — use mocktail.
• Do not test a cubit with plain test() + manual cubit.stream listening — use blocTest from bloc_test.
• Do not drop test files in a flat test/ dir — mirror the lib/feature/<feature>/... tree under test/.
• Do not skip the offline branch when testing a repository method — assert Result.failure(ServerFailure.noNetwork()) is returned and the data source is never called.