Can this method be tested using mockito? - spring-boot

Question

I am not sure how to test the first method in the service layer with Mockito as it is using the helper method. Below is my failed attempt at a test: I get an InvalidUseOfMatchersException in the second when clause.
Thanks in advance!
#Mock
private EntityRepository EntityRepo;
#InjectMocks
private EntityService EntityService;
public List<DTO> getAllDTOs(){
//first method
return entityRepo.findAll()
.stream()
.map(this::convertEntityToDTO)
.collect(Collectors.toList());
}
//helper method
public DTO convertEntityToDTO(Entity entity) {
ModelMapper modelMapper = new ModelMapper();
modelMapper.getConfiguration()
.setMatchingStrategy(MatchingStrategies.LOOSE);
DTO dto = new DTO();
dto = modelMapper.map(entity, DTO.class);
return dto;
}
#Test
public void EntityService_GetAll_ReturnsDTOList() {
when(entityRepo.findAll()).thenReturn(Mockito.anyList());
//the second when clause: when(entityService.convertEntityToDTO(Mockito.any(Entity.class)))
.thenReturn(Mockito.any(DTO.class));
List<DTO>DTOList = entityService.getAllDTOs();
Assertions.assertThat(DTOList).isNotNull();

Answer 1

Mockito#any* methods are actually defined in class ArgumentMatchers and can only be used to match the call arguments when setting up a mock or when verifying calls. All matcher methods return null (but have side-effects of modifying a matcher stack to be able to properly detect and match mocked calls).
For instance, you might do Mockito.when(svc.print(Mockito.anyString()).doNothing() when you don't care about the input or Mockito.verify(svc.print(Mockito.anyString()), Mockito.never()) when you want to verify that the method has never been called.
When setting up your mock, you have to provide a real value in your thenReturn call:
when(entityRepo.findAll()).thenReturn(Collections.emptyList());
when(entityService.convertEntityToDTO(Mockito.any(Entity.class)))
.thenReturn(new DTO());