Testing Spring Controller with Mockito-CodePudding

I am trying to learn to test using Spring 5, Mockito, and JUnit 5. I have a small normal controller class and its test is as below:

@Controller
@RequestMapping("/customer")
public class CustomerController {
    @Autowired
    CustomerService customerService;
    
    @Autowired
    CustomerForm customerForm;

    @GetMapping("/index")
    public ModelAndView index(){
        String customerName = customerService.getCustomerById(14).getFirstname();  <-- Giving me error here
        customerForm.setCustomerName(customerName);

        ModelAndView modelAndView = new ModelAndView("customer/pages/customer/Home");
        modelAndView.addObject("customerForm", customerForm);
        return modelAndView;
    }
}

@ExtendWith(MockitoExtension.class)
class CustomerControllerTest {
    
    @InjectMocks
    CustomerController customerController;
    
    @Mock
    CustomerServiceImpl customerService;
    
    @Mock
    CustomerForm customerForm;
    
    Customer customer;
    String customerName;
    
    @SuppressWarnings("deprecation")
    @BeforeEach
    void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
        customer = new Customer(14, "John");        
        customerName = "John";
    }

    @Test
    void testIndex() {
        int customerId = 14;
        when(customerService.getCustomerById(customerId).getFirstname()).thenReturn(customerName);  <-- Giving me error here, NullPointerException
        customerForm.setCustomerName(customerName);
        
        ModelAndView mav = customerController.index();
        assertEquals( customerForm, mav.getModel().get("customerForm"));
    }
}

Error:

java.lang.NullPointerException
    at com.primis.controller.CustomerControllerTest.testIndex(CustomerControllerTest.java:66)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)

When I run this test, I am getting NullPointerException as shown. Please can someone point me in the right direction, what I am doing wrong.

Thank you

CodePudding user response：

You have to mock customerService.getCustomerById(customerId) first, otherwise it will return null and, in this case, throw NPE.

CodePudding user response：

You are mocking the wrong thing:

when(customerService.getCustomerById(customerId).getFirstname()).thenReturn(customerName);

What you actually need to mock is only the call customerService.getCustomerById(). This means that your testing code should be something like:

@ExtendWith(MockitoExtension.class)
class CustomerControllerTest {
    
    @InjectMocks
    CustomerController customerController;
    
    @Mock
    CustomerServiceImpl customerService;
    
    @Mock
    CustomerForm customerForm;
    
    Customer customer;
    String customerName;
    
    @SuppressWarnings("deprecation")
    @BeforeEach
    void setUp() throws Exception {
        MockitoAnnotations.initMocks(this);
        customer = new Customer(14, "John");        
        customerName = "John";
    }

    @Test
    void testIndex() {
        int customerId = 14;
        when(customerService.getCustomerById(customerId)).thenReturn(customer);
        customerForm.setCustomerName(customerName);
        
        ModelAndView mav = customerController.index();
        assertEquals( customerForm, mav.getModel().get("customerForm"));
    }
}

As a side note, I believe that with @ExtendWith(MockitoExtension.class) you don't really need the explicit MockitoAnnotations.initMocks(this); call.