mapper in unit test is return null

Question

I have service method which return mapper to convert entity to DTO when I run the application everything work successfully but when I do unit test the mapper return null. Also I should mention that, this service is being called by another service "customerDetails" which is under the test.

code snippet, I put comments to describe the problem more :

customerService

public class customerService {

 private final CustomerMapper customerMapper;

   public Customer customerDetails(int id) {
       CustomerDto customer = getById(id) //here is the problem customer is null
       // rest of the code
     }

  public CustomerDto getById(int id) {
    Optional<Customer> customer =
        this.customerRepository.findCustomerByIdAndIsDeletedFalse(id); //assessment is filled successfully 

      return this.customerMapper.map(customer.get()); //the mapper her return customerDto and accept customer and it return null in unit test only
   }
 }

customerServiceTest

public class CustomerServiceTest {

    @Mock
    private CustomerRepository customerRepository;

    @InjectMocks
    private CustomerService customerService;

    @BeforeEach
    public void createMocks() {
       MockitoAnnotations.initMocks(this);
     }

    @Test
    public void testCustomerDetails() {
       Customer expectedResponse = DummyCustomer.create();
            when(customerRepository.findCustomerByIdAndIsDeletedFalse(actualResponse.getId()).thenReturn(Optional.of(expectedResponse));

              Customer response =   this.CustomerService.customerDetails(expectedResponse.getId());

    }
}     

Answer 1

In actual code Spring handles injection of your mapper for you - but in unit test you don't have spring context set up. In fact you'd have seen the issue earlier if instead of relying on @InjectMocks you tried to initialize the service manually.

As to solutions - in test code you can get an instance of your mapper using org.mapstruct.factory.Mappers.getMapper() method. Use it and set it in your service under test properly (however you inject your dependencies - via constructor or setter). Or, if you want a "pure" unit test of just one component, mock it.