How to use mockito to test an object which we are getting in updated form from database

Question

In my application, I am fetching customer details from an API and saving this customer to the database. after saving this customer object to in my database, I am returning customer object with id generated by the database. this is my rest Controller layer for getting customer object from API.

       //add a new customer and then return all details of newly created customer
        @PostMapping("/customer")
        public Customer addCustomer(@RequestBody Customer theCustomer)
        {
            // also just in case they pass an id in JSON ... set id to 0
            // this is to force a save of new item ... instead of update
            theCustomer.setId(0);
            return theCustomerService.saveCustomer(theCustomer);
        }

this is my service layer

@Service
public class CustomerServiceImpl implements CustomerService {

    private CustomerDAO theCustomerDAO;
    
    // set up constructor injection
    @Autowired
    public CustomerServiceImpl(CustomerDAO theCustomerDAO)
    {
        this.theCustomerDAO=theCustomerDAO;
    }

    
    @Override
    @Transactional
    public Customer saveCustomer(Customer thCustomer) {
        return theCustomerDAO.saveCustomer(thCustomer);
    }
}

and this my CustomerDAO layer where I am saving it to database

public Customer saveCustomer(Customer theCustomer)
    {
        // get the current hibernate session
        Session currentSession = entityManager.unwrap(Session.class);
        
        //save the customer
        currentSession.saveOrUpdate(theCustomer);
        
        return theCustomer;
    }

above parts of my Application are working properly but now I want to add testing in it. so I created a test method for the service layer.

class CustomerServiceImplTest {
    @Test
    void saveCustomer() {

        CustomerDAO theCustomerDAO=mock(CustomerDAO.class);
        CustomerServiceImpl theCustomerServiceImpl=new CustomerServiceImpl(theCustomerDAO);

        Customer inCustomer=new Customer("john","nick","google@gmail.com","CPOI939","8607574640");
        inCustomer.setId(0);
        Customer outCustomer=inCustomer;
        outCustomer.setId(9);
        when(theCustomerDAO.saveCustomer(inCustomer)).thenReturn(outCustomer);
        assertEquals(outCustomer,theCustomerServiceImpl.saveCustomer(inCustomer));
    }
}

But I am not sure that it's a good way of testing because we are not adding any business logic in the service layer. so how do I test it and which layer should be tested.

Answer 1

Try to test this case on the integration level. There is no business logic just pure crud to save data to DB.

You can use DbUnit and in-memory databases like H2 .

DbUnit is a JUnit extension targeted at database-driven projects that, among other things, puts your database into a known state between test runs.

example test:

@Test
@DatabaseSetup("sampleData.xml")
public void testSaveCustomer() throws Exception {
    Customer inCustomer=new Customer("john","nick","google@gmail.com","CPOI939","8607574640");
    
    theCustomerServiceImpl.saveCustomer(inCustomer) 
    
    List<Customer> customerList = customerService.findAll();
    assertEquals(1, customerList.size());
    assertEquals("john", customerList.get(0).getName());
    ...
} 

More details Spring nad DBUnit