How to mock default method of unimplemented interface?

Question

I'm doing some hands on with Junit/Mockito/PowerMockito

I have an interface class

import retrofit2.Call;
import com.learning.model.user.User;
import java.io.IOException;

public interface UserService {
        @GET("/serviceUser/{userId}")
        Call<User> getUser(@Path("userId") String userId);
    
        default User getUserById(String userId) {
            try {
                return getUser(userId).execute().body();
            } catch (IOException e) {
                e.printStackTrace();
                return null;
            }
        }

        static UserService getUserService(){
            //setup retrofit ...
        }
}

In another service:

public class DemoUser {
    public void doUserBusiness(String userId) {
        User user = UserService.getService().getUserById(userId);
        //do business logic here
    }
}

Then how can I mock the UserService.getService().getUserById(userId); to return a mock user when testing the doUserBussiness method?

Answer 1

You can try to use mockStatic() like:

try (MockedStatic<UserService> serviceMockedStatic = mockStatic(UserService.class)) {
     serviceMockedStatic
         .when(() -> UserService.getService().getUserById(userId))
         .thenReturn(any());
}

More here -> staticMock