The solution is simple. You mocked a class customerDataRepository but did not instruct it the mock what to do if the corresponding method is called. Mockito mocks then default back on doing nothing by method call and if there is a return value return null. Since your returned customerData is null you get your NPE when calling on this object. In your case this is in the error case that you get by calling getCustomerId().

To solve this issue simply instruct your mock

@Test
void removeCustomerDataWhenConsentIsNotGiven() {
   CustomerData customerDataTest = customerData;
   //when
   Mockito.when(customerDataRepository.findCustomerByDialogId(Mockito.any())).thenReturn(new CustomerData()); // <-- Add this line
   customerDataService.giveConsent(false,22L);
   //then 
   verify(customerDataRepository,times(1)).save(customerDataTest);
}

you can obviously replace Mockito.any() with Mockito.anyInt() or 42 and new CustomerData() with a object you previously created. I think you get the idea ;)

I had this issue and my problem was that I was calling my method with any() instead of anyInt(). So I had:

doAnswer(...).with(myMockObject).thisFuncTakesAnInt(any())

and I had to change it to:

doAnswer(...).with(myMockObject).thisFuncTakesAnInt(anyInt())

I have no idea why that produced a NullPointerException. Maybe this will help the next poor soul.

I think calling mock(YourClass.class) returns a mock which upon calling its methods throws a NPE. This mean you should explicitly use doCallRealMethod(yourMock).when(yourMethod()) if you want the mock's method to behave like it normally would. By calling Mockito.spy(YourClass.class) it will create a mock which by default uses the real methods, if you don't specify otherwise

You are trying to mock two methods at once. In this line:Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);you are calling get() on the result of the createValueProducer() call, which is null because you haven’t mocked it yet.There are two solutions:Use deep stubbing:ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class, Mockito.RETURNS_DEEP_STUBS);Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList()).get()).thenReturn(mappedValue);Mock the Supplier first (pay attention to the removed get()):Supplier supplier = () -> mappedValue;ValueProducerFactory valueProducerFactory = Mockito.mock(ValueProducerFactory.class);Mockito.when(valueProducerFactory.createValueProducer("IdProducer", Collections.emptyList())).thenReturn(supplier);

You should call MockitoAnnotations.initMocks(this) in your setup method:

  @Before
public void setUp() throws Exception {
    calendarDto = new ArrayList<CalendarDto>();
    test1 = new CalendarDto();
    test1.setStatus(TimesheetStatusEnum.APPROVED);
    test1.setMonth(1);
    test2 = new CalendarDto();
    test2.setMonth(2);
    test2.setStatus(TimesheetStatusEnum.REJECTED);
    calendarDto.add(test1);
    calendarDto.add(test2);

    MockitoAnnotations.initMocks(this)
}

You need to do below fixes in your test case and then your issue will be resolved.

1. Add @ExtendWith(MockitoExtension.class) annotation on top of TaskServiceTest class.
2. Replace @MockBean annotation with @Mock on top of TaskRespository instance.
3. Remove @Autowired annotation on top of TaskService instance.
4. Mock save() method of TaskRepository class and then call createTask() method in test case.