State notifier test - A testing library which makes it easy to test StateNotifier. Built to be used with the state notifier, riverpod or flutter riverpod packages

If the StateNotifier's constructor calls some method that will update the state it will interfere with the method being called directly in the actions callback of the test itself.

For example if in the StateNotifier we have a constructor and method we would like to test like below:

class ExampleStateNotifier extends StateNotifier<ExampleState> {
  final ExampleRepository _recipeRepository;
  ExampleStateNotifier(this._exampleRepository)
      : super(const ExampleState.initial()) {
    loadExampleString();
  }

  Future<void> loadExampleString() async {
    state = const ExampleState.loading();
    final result = await _exampleRepository.loadExampleString();
    state = result.fold(
        (failure) => ExampleState.error(error: failure.failureMessage()),
        (data) => ExampleState.loaded(string: data.string ?? ''));
  }
}

Now if we want in the test to test loadExampleString() method, because loadExampleString() is also being called from the constructor we won't get expected states in the test, ExampleState.loading() and ExampleState.loaded(string: string). By adding a short delay after build() method is called in the testNotifier() method, loadExampleString() call from the constructor will be ignored and then when testing loadExampleString() we will be able to get the exact states we are expecting.

The proposed solution then is to add new attribute ignoreBuildCalls when instantiating stateNotifierTest class and adding a short delay (100 ms should be enough for testing with mock repository) after the build() method is being called.

If you see a different and perhaps better solution for the described problem, feel free to share it :)

Other similar solution that comes to my mind is to introduce just afterBuild optional Future callback that could be await executed after the build() call to maybe have a little bit more options in defining how long this delay should be. On the other hand ignoreBuildCalls attribute is maybe more clear how to use it but I would also like to hear your opinion on that.

Kind regards, Ivan Celija

Hi there! I run in a little problem while trying to create a test for my UserNotifier (StateNotifier).

This is the constructor of stateNotifierTest:

void stateNotifierTest<SN extends StateNotifier<State>, State>(
  String description, {
  required FutureOr Function(SN stateNotifier) actions,
  FutureOr<void> Function()? setUp,
  FutureOr<void> Function(SN stateNotifier)? verify,
  FutureOr<void> Function()? tearDown,
  required List<State> Function() expect,
  Iterable<State> Function()? seed,
  int skip = 0,
  required SN Function() build,
  dynamic Function()? errors,
  bool expectInitialState = false,
}) { ...

You mentioned in the comment above that we can use expect with isA<>() type matcher, but it is not possible with the current constructor declaration.

/// **Note:** when using [stateNotifierTest] with state classes which don't override
/// `==` and `hashCode` you can provide an `Iterable` of matchers instead of
/// explicit state instances.
///
/// ```dart
/// stateNotifierTest(
///  'emits [StateB] when EventB is called',
///  build: () => MyBloc(),
///  action: (stateNotifier) => stateNotifier.add(EventB()),
///  expect: () => [isA<StateB>()],
/// );
/// ```

So while trying to start the test like this:

stateNotifierTest<UserNotifier, AsyncValue<User?>>(
  'returns error when trying to edit a null user',
  expectInitialState: false,
  build: () => UserNotifier(
    userId: null,
    userRepository: mockUserRepository,
  ),
  actions: (un) {
    un.editUser(user1);
  },
  expect: () => [isA<AsyncError>()],
);

I get this error

Removing the type doesn't work either.

I think being able to pass isA<>()would be very useful, since I have the editUser method that returns an AsyncValue.error, which requires the error object and also the current StackTrace, which is impossible to recreate as an object. I saw that there is an errors parameter, but still, since expect is required and must match exactly the test will fail.

Thank you!

I'm trying to port the counter bloc example test link to Riverpod and the tests, bloc_test uses MockBloc/MockCubit to achieve this like this:

class MockCounterCubit extends MockCubit<int> implements CounterCubit {}
void main() {
late CounterCubit counterCubit;

  setUp(() {
    counterCubit = MockCounterCubit();
  });

testWidgets('renders current CounterCubit state', (tester) async {
      when(() => counterCubit.state).thenReturn(42);
      await tester.pumpWidget(
        MaterialApp(
          home: BlocProvider.value(
            value: counterCubit,
            child: CounterView(),
          ),
        ),
      );
      expect(find.text('42'), findsOneWidget);
    });
}

What I got is this:

class CounterProvider extends StateNotifier<int> {
  CounterProvider() : super(0);

  void increment() => state = state + 1;

  void decrement() => state = state - 1;
}

class MockCounterStateNotifier extends Mock implements CounterProvider {}
void main() {
  late CounterProvider counterProvider;

  setUp(() {
    counterProvider = MockCounterStateNotifier();
  });

  group('CounterView', () {
    testWidgets('renders current Counter state', (tester) async {
      //when(() => counterProvider.state).thenReturn(42);
      await tester.pumpWidget(
        const ProviderScope(
          child: MaterialApp(home: CounterPage()),
        ),
      );
      expect(find.text('42'), findsOneWidget);
    });
  });
}