Unit Tests How to Mock Repository Using Mockito

Question

I am having an issue with stubbing my repository. I was suggested to just create another application.properties (which I have not done) and to use an in-memory database like H2. I was wondering though if I can just stub the call so when myDataService.findById(id) is called instead of it attempting to get that from the database just a mocked object can be returned?

I am new to writing mocks for my unit tests and spring boot in general so maybe I am missing something. Code below (tried to simplify and made names generic for posting here).

My test class

public class MyServiceImplTest 
{
    private MyDataService myDataService;
    private NyService myService;
    private MyRepository myRepository;

    @Before
    public void setUp() {
        myDataService = Mockito.mock(MyDataServiceImpl.class);
        myService = new MyServiceImpl(myDataService);
    }

    @Test
    public void getById_ValidId() {
        doReturn(MyMockData.getMyObject()).when(myDataService).findById("1");
        when(myService.getById("1")).thenReturn(MyMockData.getMyObject());
        MyObject myObject = myService.getById("1");

        //Whatever asserts need to be done on the object myObject 
    }
}

Class used for making the service call to the data layer

@Service
public class MyServiceImpl implements MyService {
    MyDataService myDataService;

    @Autowired
    public MyServiceImpl(MyDataService myDataService) {
        this.myDataService = myDataService;
    }

    @Override
    public MyObject getById(String id) {
        if(id == null || id == "") {
            throw new InvalidRequestException("Invalid Identifier");
        }

        MyObject myObj;
        try {
            myObj = myDataService.findById(id);
        }catch(Exception ex) {
            throw new SystemException("Internal Server Error");
        }

        return myObj;
    }
}

This is where I am having the issue in my test. When the findById() method is called, the variable repository is null so when trying to do repository.findOne(id) it throws an exceptionn. This is what I am attempting to mock, but the repository is giving me issues.

@Repository
@Qualifier("MyRepo")
public class MyDataServiceImpl {

    @PersistenceContext
    private EntityManager em;

    private MyRepository repository;

    @Autowired
    public MyDataServiceImpl(MyRepository repository) {
        super(repository);
        this.repository = repository;
    }

    public MyObject findById(String id) {
        P persitentObject = repository.findOne(id);
        //Calls to map what persitentObject holds to MyObject and returns a MyObject 
    }
}

Code for MyRepository here just to show it's an empty interface that extends CrudRepository

public interface MyRepository extends CrudRepository<MyObjectPO, String>, JpaSpecificationExecutor<MyObjectPO> {

}

Answer 1

Let me begin by saying you are on the right track by using Constructor Injection and not Field Injection(which makes writing tests with mocks much simpler).

public class MyServiceImplTest 
{
    private MyDataService myDataService;
    private NyService myService;

    @Mock
    private MyRepository myRepository;

    @Before
    public void setUp() {
        MockitoAnnotations.initMocks(this); // this is needed for inititalizytion of mocks, if you use @Mock 
        myDataService = new MyDataServiceImpl(myRepository);
        myService = new MyServiceImpl(myDataService);
    }

    @Test
    public void getById_ValidId() {

        doReturn(someMockData).when(myRepository).findOne("1");
        MyObject myObject = myService.getById("1");

        //Whatever asserts need to be done on the object myObject 
    }
}

The call goes all the way from your service --> dataService. But only your repository calls are mocked.
This way you can control and test all the other parts of your classes(both service and dataService) and mock only repository calls.