NullPointerException while I'm trying to unit test Spring Boot Application

Question

When I try to test my CRUD operations in my Spring Boot Applications, I get NullPointerException saying that this.Repository is null. What can I do to resolve this issue? Am I missing something?

My test class:

@RunWith(MockitoJUnitRunner.class)
class AppointmentServiceTest {
 @Mock
 private AppointmentRepository appointmentRepository;
 @InjectMocks
 private AppointmentService appointmentService;
 @Test
 void shouldGetAllAppointments() {
 List<Appointment> appointments = new ArrayList<>();
 appointments.add(new Appointment());
 given(appointmentRepository.findAll()).willReturn(appointments);
 List<Appointment> expectedAppointments = appointmentService.getAllAppointments();
 assertEquals(expectedAppointments, appointments);
 verify(appointmentRepository.findAll());
 }
}

I am getting NullPointerException:

java.lang.NullPointerException: Cannot invoke "com.app.hospitalmanagementsystem.repository.AppointmentRepository.findAll()" because "this.appointmentRepository" is null

• Mark Bramnik: what are given and verify methods? To which library do they belong? Probably makes sense to add a corresponding tag
• nikolaPantelic98: Hello, given is from org.mockito.BDDMockito and verify is from org.mockito.Mockito . Maybe the issue is caused by wrong static imports?
• Mark Bramnik: I haven't worked with BDDMockito. You can try Mockito.when(appointmentRepository.findAll()).thenReturn(appointments); Also, Are you sure you're running with JUnit 4 I mean is it your real intention? Or you need JUnit 5 really?
• nikolaPantelic98: Hey, you are right. I was trying to run with JUnit4 while I needed JUnit5. I just replaced @RunWith() with @DataJpaTest and it works fine. Thank you.
• Mark Bramnik: @DataJpaTest is a compeletely different beast :) Its not even a unit test anymore, it runs Spring infrastructure with real repositories, so make sure you understand the difference. For plain Unit test powered by JUnit 5, use @ExtendsWIth(MockitoExtension.class)

Answer 1

Since the spring boot is tagged here, the chances that you're using spring boot 2.x (1.x is outdated these days)

But if so, you should be running JUnit 5 tests (spring boot 2.x works with Junit 5)

So instead of @RunWith annotation, use @ExtendsWith

Then place the breakpoint in the test and make sure that mockito extension has actually worked and the mock is created.

Now as for the given - I can't say for sure, I haven't used this syntax (BDD Mockito), but in a "clean mockito" it should be Mockito.when(..).thenReturn

All-in-all try this code:

@ExtendsWith(MockitoExtension.class)
class AppointmentServiceTest {
 @Mock
 private AppointmentRepository appointmentRepository;
 @InjectMocks
 private AppointmentService appointmentService;
 @Test
 void shouldGetAllAppointments() {
 List<Appointment> appointments = new ArrayList<>();
 appointments.add(new Appointment());
 Mockito.when(appointmentRepository.findAll()).thenReturn(appointments);
 List<Appointment> expectedAppointments = appointmentService.getAllAppointments();
 assertEquals(expectedAppointments, appointments);
 verify(appointmentRepository.findAll());
 }
}