# 引数に応じた返り値の変更

例えば以下のような場合に、`FindProfileUseCase#execute` から返される Profile を id に応じて変えたいとします。

```dart
class ProfileViewModel {
  ProfileViewModel({
    required FindProfileUseCase findProfileUseCase,
  }) : _findProfileUseCase = findProfileUseCase;

  final FindProfileUseCase _findProfileUseCase;

  Profile _profile = Profile.empty;

  int get id => _profile.id;

  void onIdChanged(int id) {
    _profile = _findProfileUseCase.execute(id: id);
  }
}

class Profile {
  const Profile({
    required this.id,
    required this.groupId,
    required this.name,
    required this.thumbnailUrl,
    required this.location,
  });

  ...
}

class FindProfileUseCase {
  Profile execute({required int id}) { ... }
}
```

## Recipe

### thenAnswer

`thenAnswer` を使用して `realInvocation` を見ることで引数を取得することができます。

```dart
test('test', () {
  when(findProfileUseCase.execute(id: anyNamed('id'))).thenAnswer(
    (realInvocation) => Profile(
      id: realInvocation.namedArguments[#id] as int,
      groupId: 0,
      name: 'name',
      thumbnailUrl: 'thumbnailUrl',
      location: 'location',
    ),
  );

  viewModel.onIdChanged(2);

  expect(viewModel.id, 2);
});
```

## Result

```dart
@GenerateMocks([
  FindProfileUseCase,
])
void main() {
  late MockFindProfileUseCase findProfileUseCase;
  late ProfileViewModel viewModel;

  setUp(() {
    findProfileUseCase = MockFindProfileUseCase();
    viewModel = ProfileViewModel(
      findProfileUseCase: findProfileUseCase,
    );
  });

  test('test', () {
    when(findProfileUseCase.execute(id: anyNamed('id'))).thenAnswer(
      (realInvocation) => Profile(
        id: realInvocation.namedArguments[#id] as int,
        groupId: 0,
        name: 'name',
        thumbnailUrl: 'thumbnailUrl',
        location: 'location',
      ),
    );

    viewModel.onIdChanged(2);

    expect(viewModel.id, 2);
  });
}
```


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