Why is there no spy functionality in Mockito Dart?

tobyres 0
Viewed 29

The following code is a simplified example from my code. I have class A which is dependent on class B. I want to test class A, so I mock class B. Then I'm writing a test for a method of class A and inside of that test I write a stub for whenever a method from my mocked class B is called:

fetchData() async {
try {
  await b.getData();
}  on DioError catch (e) {
  switch (e.response!.statusCode) {
    case 401:
      logout();
      throw UnauthorizedException();
    default:
      throw UnspecifiedDioException(error: e);
  }
}

Test written for fetchData() method:

test('check if fetchData calls logout when 401 is returned', () {

     when(mockB.getData())
         .thenAnswer((_) async =>
         throw DioError(
             requestOptions: RequestOptions(path: ""),
             response: Response(requestOptions: RequestOptions(path: ""), statusCode: 401)));

     verify(a.logout()); // doesn't work because A isn't mocked
});

I've read that you can do this very easily with spies but to my surprise spies are available for every language which uses mockito except for dart. It's apparently deprecated but then again how can something be deprecated if there isn't even a newer version to replace it with.

I'd really appreciate it if someone could tell me if there is a convenient workaround for what I'm trying to achieve. Thanks in advance.

Edit: I've changed the question because the former one wasn't making much sense. I just wanna know if there is something like spies in dart or not.

mockito dart testing
1 Answers

Using mocktail.. You should stub your logout invocation's dependency as well.


class A {
  A({required this.api, required this.auth});

  // to be mocked
  final Api api;
  final Auth auth;

  Future<void> fetchData() async {
    try {
      await api.getData();
    } catch (e) {
      auth.logout();
    }
  }
}

class Auth {
  Future<void> logout() => Future(() {});
}

class Api {
  Future<void> getData() => Future(() {});
}

And your test

class MockApi extends Mock implements Api {}

class MockAuth extends Mock implements Auth {}

void main() {
  // create mock objects
  final mockApi = MockApi();
  final mockAuth = MockAuth();

  test('when [Api.getData] throws, [Auth.logout] is called', () async {
    // create an instance of "A" and use your mock objects
    final a = A(api: mockApi, auth: mockAuth);

    // use "thenThrow" to throw
    when(() => mockApi.getData()).thenThrow('anything');
    // use "thenAnswer" for future-returning methods
    when(() => mockAuth.logout()).thenAnswer((_) => Future.value(null));

    // call the method to "start" the test
    await a.fetchData();

    // verify logout was called
    verify(mockAuth.logout).called(1); // passes
  });
}
Apealed0
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