Can dart Mockito mock abstract classes?

user_16261841 0
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I am trying to add some unit tests to my dart/flutter library, and one of the dependencies of my unit-under-test is an abstract class:

abstract class LoginService {
    Future<void> login(String username, String password);
}

When I add @GenerateMocks([LoginService]) to my test file and run build_runner, it fails with:

mockito:mockBuilder on test/login_test.dart:  Invalid @GenerateMocks annotation: The GenerateMocks "classes" argument is missing, includes an unknown type, or includes an extension

But if I manually type:

class MockLoginService extends Mock implements LoginService {}

there is no compilation error.

If I change LoginService to no longer be abstract (with some dummy implementation), then the mock succeeds.

Any ideas? I've checked dart Mockito's GitHub issues but can't find anyone with this issue.

dart flutter mockito
2 Answers

I used mockito to mock for an abstract repository. E.g;

@GenerateMocks([NumberTriviaRepository])
void main(){
  final mockNumberTriviaRepository = MockNumberTriviaRepository();
}

Use build_runner to generate files;

flutter packages pub run build_runner build --delete-conflicting-outputs
user_80952700

If the example code from the mockito_builder repo is any indication, it seems like in order to build mocks of abstract classes, there needs to be a concrete implementation of that class somewhere.

My guess is that, when the Dart code is compiled (JIT or otherwise) and loaded into the build_runner, tree-shaking will see that the abstract class has no implementations nor any other references of any kind, so it removes the class from the compiled code. By the time build_runner can do its thing, the abstract class effectively no longer exists.

So in theory, all you need to do is make a placeholder implementation of your class and the code generation will work:

abstract class LoginService {
  Future<void> login(String username, String password);
}

class LoginServiceImpl extends LoginService {
  @override
  Future<void> login(String username, String password) {
    throw UnimplementedError();
  }
}
user_12558730
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