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

what are given and verify methods? To which library do they belong? Probably makes sense to add a corresponding tag — Mark Bramnik
– Mark Bramnik, Commented Aug 21, 2022 at 12:12
Hello, given is from org.mockito.BDDMockito and verify is from org.mockito.Mockito . Maybe the issue is caused by wrong static imports? — nikolaPantelic98
– nikolaPantelic98, Commented Aug 21, 2022 at 12:19
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? — Mark Bramnik
– Mark Bramnik, Commented Aug 21, 2022 at 12:47
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. — nikolaPantelic98
– nikolaPantelic98, Commented Aug 21, 2022 at 13:05
@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) — Mark Bramnik
– Mark Bramnik, Commented Aug 21, 2022 at 13:38

Mark Bramnik · Accepted Answer · 2022-08-21 13:54:52Z

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());
    }
}

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