What repository will return when object not found in tests

My question is : what repository will return when object not found in
junit tests.

I have test like this :

@RunWith(MockitoJUnitRunner.class)
@SpringBootTest
public class CouponServiceTestSuite {
    private final static String HOME_TEAM = "home team";
    private final static String AWAY_TEAM = "away team";
    @Autowired
    private CouponService couponService;
    @MockBean
    private CouponRepository couponRepository;
    @MockBean
    private MatchRepository matchRepository;
    @Test
    public void shouldThrowException() {
        //Given
        //When
        //Then
        Assertions.assertThrows(BetWinnerException.class, () -> couponService.getCoupon(-6L));

I want to mock this like :

Mockito.when(couponRepository.findById(ArgumentMatchers.anyLong()).thenReturn(null);

My service class :

@Slf4j
@RequiredArgsConstructor
@Service
public class CouponService {
    private final CouponRepository couponRepository;
    private final MatchRepository matchRepository;
    private final CouponMapper couponMapper;

    public List<CouponDto> getCoupons() {
        log.debug("Getting all coupons");
        List<Coupon> couponList = couponRepository.findAll();
        List<CouponDto> couponDtoList = couponMapper.mapToCouponDtoList(couponList);
        log.debug("Return all coupons: {}", couponDtoList);
        return couponDtoList;
    }

    public CouponDto getCoupon(Long couponId) {
        log.debug("Getting coupon by id: {}", couponId);
        Coupon coupon = couponRepository.findById(couponId).orElseThrow(()
                -> new BetWinnerException(BetWinnerException.ERR_COUPON_NOT_FOUND_EXCEPTION));
        CouponDto couponDto = couponMapper.mapToCouponDto(coupon);
        log.debug("Return coupon: {}", couponDto);
        return couponDto;
    }

    public CouponDto createCoupon() {
        log.debug("Creating new coupon");
        Coupon coupon = couponRepository.save(new Coupon());
        CouponDto couponDto = couponMapper.mapToCouponDto(coupon);
        log.debug("Return created coupon: {}", couponDto);
        return couponDto;
    }

    public CouponDto addMatch(Long couponId, Long matchId) {
        log.debug("Add match to the coupon: {}{}", matchId, couponId);
        Coupon coupon = couponRepository.findById(couponId).orElseThrow(()
                -> new BetWinnerException(BetWinnerException.ERR_COUPON_NOT_FOUND_EXCEPTION));
        Match match = matchRepository.findById(matchId).orElseThrow(()
                -> new BetWinnerException(BetWinnerException.ERR_MATCH_NOT_FOUND_EXCEPTION));
        coupon.getMatchList().add(match);
        Coupon updatedCoupon = couponRepository.save(coupon);
        CouponDto couponDto = couponMapper.mapToCouponDto(updatedCoupon);
        log.debug("Return coupon with added match: {}", couponDto);
        return couponDto;
    }

    public boolean deleteCoupon(Long couponId) {
        log.debug("Deleting coupon id: {}", couponId);
        couponRepository.deleteById(couponId);
        if (couponRepository.existsById(couponId)) {
            log.debug("Coupon not deleted id: {}", couponId);
            return false;
        } else {
            log.debug("Coupon deleted id: {}", couponId);
            return true;
        }
    }
}

I thought that it returns null but when i do like this it returns NullPointerException. My service returns BetWinnerException when object is not found.
So what it will return ? How should i create this test ?

Test like this works properly but i dont want to use id = -6. I just want to mock it somehow.

Please post your entire test class

Add @InjectMocks annotation above the @Autowired in the service you declared in your test and see if it solves the problem, however I don't think it will work considering you have your Repo declared as FINAL in your Service. If it`s not FINAL and is @Autowired, the InjectMocks would work fine for your mock. But if you really need this as FINAL, try this:

https://www.baeldung.com/mockito-final

You are mocking couponRepository but using couponService and as there is no code shown how that is initialised in your test, it is hard to tell, where the problem is.

Now that you updated your question, the answer is quite obvious:

• in the service the code expects couponRepository.findById() to return an Optional so that it can throw the exception if that is empty
• mocked beans are 'normal' Mockito mocks that try to return a useful result; for collection this is an empty collection, for objects this is null - usually
• TIL that Mockito 2 will support what you expect: https://www.baeldung.com/mockito-2-java-8#return-default-values-for-optional-and-stream
• this article also shows how to make Mockito 1 return the empty Optional
• you tried to make it return null but you actually need Optional.empty()

Or did I misunderstand how you actually test it and what your problem is?

• Do you get a NullPointerException in the service as I understood?
• Or do you already use Mockito 2 and have another issue?