Flutter Mockito. Failing to mock

Question

I am trying to use mockito in my project to test an API. Here is a small snippet code under organization_test.dart. I will only provide up until the error line as it is the only concern.

class MockOrganizationRemoteDataSource extends Mock implements OrganizationRemoteDataSource {}


void main(){
 late final MockOrganizationRemoteDataSource mockOrganizationDataSource;
 late final IOrganizationRepository iOrganizationRepository;
 final tOrgName = "someOrgName";

 setUp((){
  mockOrganizationRemoteDataSource = MockOrganizationRemoteDataSource();
  iOrganizationRepository = IOrganizationRepository(mockOrganizationRemoteDataSource);
 });

 test("Should fetch the organization",() async {
  when(mockOrganizationRemoteDataSource.getOrganization(tOrgName)) // Getting ERROR on this line
   .thenAnswer(
      (_) async => Response(
       requestOption: RequestOption(
        path: <Some url in here 👌🏼>
        data: <Some json response here 👌🏼>
        responseType: ResponseType.json)
      ),
   );
 
   final result = await iOrganizationRepository.fetchOrganization(tOrgName);   
   
   ...
   ... // some more code here


 });
}

Then I get error is type 'Null' is not a subtype of type 'Future<Response<dynamic>>'

I was expecting that if I use mock I can call the getOrganization method from the mockedDataSource and pretend to answer a response. Yet upon debugging this, I always ending up referencing to the Un-mocked class which is the OrganizationRemoteDataSource resulting the null value.

BTW I'm using flutter with null-safety enabled and Dio.

Solution

Thanks to jamesdlin's comment I was able to resolve this:

• Add @GenerateMocks annotation to the void main()

@GenerateMocks([OrganizationRemoveDataSource])
void main(){
...
}

• Removed the MockOrganizationRemoteDataSource class and used the build_runner to allow Mockito to generate the annotated GenerateMocks.

UPDATE:

Due to the intricacy of using Mockito in a null-safety dart. I came across a great library that works as alternative named Mocktail. You can see the library here https://pub.dev/packages/mocktail.

Comments

[jamesdlin]

Did you follow the null-safety instructions and call @GenerateMocks?

[GhoSt]

Apparently, I have not and doesn't know that. Will check now. Thanks! I'll ask again if I still get the same error.

[GhoSt]

Thanks @jamesdlin! It worked using the @GenerateMocks.