Mockito & Junit5

Advanced Mockito

Controller Test

A way to capture the information going into the argument of the mock, in other words, to look at the value that is passed in.

When there is a class which takes in a property and then modifies that property.
Then we can do assertions to make sure that modification of the property which has been passed in is actually correct.

OwnerController

public class OwnerController {

    private final OwnerService ownerService;

    public String processFindForm(Owner owner, BindingResult result, Model model){
        // allow parameterless GET request for /owners to return all records
        if (owner.getLastName() == null) {
            owner.setLastName(""); // empty string signifies broadest possible search
        }

        // find owners by last name
        List<Owner> results = ownerService.findAllByLastNameLike("%"+ owner.getLastName() + "%");

        if (results.isEmpty()) {
            // no owners found
            result.rejectValue("lastName", "notFound", "not found");
            return "owners/findOwners";
        } else if (results.size() == 1) {
            // 1 owner found
            owner = results.get(0);
            return "redirect:/owners/" + owner.getId();
        } else {
            // multiple owners found
            model.addAttribute("selections", results);
            return "owners/ownersList";
        }
    }
}

OwnerControllerTest

@ExtendWith(MockitoExtension.class)
class OwnerControllerTest {

    private static final String OWNERS_CREATE_OR_UPDATE_OWNER_FORM = "owners/createOrUpdateOwnerForm";
    private static final String REDIRECT_OWNERS_5 = "redirect:/owners/5";

    @Mock
    OwnerService ownerService;

    @InjectMocks
    OwnerController controller;

    @Mock
    BindingResult bindingResult;
    @Test
    void processCreationFormHasErrors() {
        //given
        Owner owner = new Owner(1l, "Jim", "Bob");
        given(bindingResult.hasErrors()).willReturn(true);

        //when
        String viewName = controller.processCreationForm(owner, bindingResult);

        //then
        assertThat(viewName).isEqualToIgnoringCase(OWNERS_CREATE_OR_UPDATE_OWNER_FORM);
    }

    @Test
    void processCreationFormNoErrors() {
        //given
        Owner owner = new Owner(5l, "Jim", "Bob");
        given(bindingResult.hasErrors()).willReturn(false);
        given(ownerService.save(any())).willReturn(owner);

        //when
        String viewName = controller.processCreationForm(owner, bindingResult);

        //then
        assertThat(viewName).isEqualToIgnoringCase(REDIRECT_OWNERS_5);
    }
}

ArgumentCaptor

A way to capture the information going into the argument of the mock, in other words, to look at the value that is passed in.

When there is a class which takes in a property and then modifies that property.
Then we can do assertions to make sure that modification of the property which has been passed in is actually correct.

@ExtendWith(MockitoExtension.class)
class OwnerControllerTest {

    // ...

    @Captor
    ArgumentCaptor<String> stringArgumentCaptor;

    @Test
    void processFindFormWildcardString() {
        //given
        Owner owner = new Owner(1l, "Joe", "Buck");
        List<Owner> ownerList = new ArrayList<>();

        // Manually create a captor
        final ArgumentCaptor<String> captor = ArgumentCaptor.forClass(String.class);
        given(ownerService.findAllByLastNameLike(captor.capture())).willReturn(ownerList);

        //when
        String viewName = controller.processFindForm(owner, bindingResult, null);

        //then
        assertThat("%Buck%").isEqualToIgnoringCase(captor.getValue());
    }

    @Test
    void processFindFormWildcardStringAnnotation() {
        //given
        Owner owner = new Owner(1l, "Joe", "Buck");
        List<Owner> ownerList = new ArrayList<>();

        // In an annotation way 
        given(ownerService.findAllByLastNameLike(stringArgumentCaptor.capture())).willReturn(ownerList);

        //when
        String viewName = controller.processFindForm(owner, bindingResult, null);

        //then
        assertThat("%Buck%").isEqualToIgnoringCase(stringArgumentCaptor.getValue());
    }
}

willAnswer

What willAnswer allows us to do is get a hold of the actual invocation of the mock and make some decisions about it.
It compares very closely to ArgumentCaptor but it's kind of combining what we are gonna return from the mock. So the answer functionality

OwnerController

public class OwnerController {
    private final OwnerService ownerService;
    public String processFindForm(Owner owner, BindingResult result, Model model){
        // allow parameterless GET request for /owners to return all records
        if (owner.getLastName() == null) {
            owner.setLastName(""); // empty string signifies broadest possible search
        }

        // find owners by last name
        List<Owner> results = ownerService.findAllByLastNameLike("%"+ owner.getLastName() + "%");

        // Three different test scenarios
        if (results.isEmpty()) {
            // no owners found
            result.rejectValue("lastName", "notFound", "not found");
            return "owners/findOwners";
        } else if (results.size() == 1) {
            // 1 owner found
            owner = results.get(0);
            return "redirect:/owners/" + owner.getId();
        } else {
            // multiple owners found
            model.addAttribute("selections", results);
            return "owners/ownersList";
        }
    }
}

OwnerControllerTest

@ExtendWith(MockitoExtension.class)
class OwnerControllerTest {

    @Mock
    OwnerService ownerService;

    @InjectMocks
    OwnerController controller;

    @Mock
    BindingResult bindingResult;

    @Captor
    ArgumentCaptor<String> stringArgumentCaptor;

    @BeforeEach
    void setUp() {
        given(ownerService.findAllByLastNameLike(stringArgumentCaptor.capture()))
                .willAnswer(invocation -> {
            List<Owner> owners = new ArrayList<>();

            String name = invocation.getArgument(0);

            // Three different test scenarios
            if (name.equals("%Buck%")) {
                owners.add(new Owner(1l, "Joe", "Buck"));
                return owners;
            } else if (name.equals("%DontFindMe%")) {
                return owners;
            } else if (name.equals("%FindMe%")) {
                owners.add(new Owner(1l, "Joe", "Buck"));
                owners.add(new Owner(2l, "Joe2", "Buck2"));
                return owners;
            }

            throw new RuntimeException("Invalid Argument");
        });
    }

    @Test
    void processFindFormWildcardFound() {
        //given
        Owner owner = new Owner(1l, "Joe", "FindMe");

        //when
        String viewName = controller.processFindForm(owner, bindingResult, Mockito.mock(Model.class));

        //then
        assertThat("%FindMe%").isEqualToIgnoringCase(stringArgumentCaptor.getValue());
        assertThat("owners/ownersList").isEqualToIgnoringCase(viewName);
    }

    @Test
    void processFindFormWildcardStringAnnotation() {
        //given
        Owner owner = new Owner(1l, "Joe", "Buck");

        //when
        String viewName = controller.processFindForm(owner, bindingResult, null);

        //then
        assertThat("%Buck%").isEqualToIgnoringCase(stringArgumentCaptor.getValue());
        assertThat("redirect:/owners/1").isEqualToIgnoringCase(viewName);
    }
    
    @Test
    void processFindFormWildcardNotFound() {
        //given
        Owner owner = new Owner(1l, "Joe", "DontFindMe");

        //when
        String viewName = controller.processFindForm(owner, bindingResult, null);

        //then
        assertThat("%DontFindMe%").isEqualToIgnoringCase(stringArgumentCaptor.getValue());
        assertThat("owners/findOwners").isEqualToIgnoringCase(viewName);
    }
}

Debugging the method @Test void processFindFormWildcardFound()

InOrder

Verify the order of the mock interactions,and specify that these mocks need to be called in the specific order.

    @Test
    void processFindFormWildcardFound() {
        //given
        Owner owner = new Owner(1l, "Joe", "FindMe");
        InOrder inOrder = inOrder(ownerService, model);

        //when
        String viewName = controller.processFindForm(owner, bindingResult, model);

        //then
        assertThat("%FindMe%").isEqualToIgnoringCase(stringArgumentCaptor.getValue());
        assertThat("owners/ownersList").isEqualToIgnoringCase(viewName);

        // inorder asserts
        // To make sure that service is called before the model is called
        inOrder.verify(ownerService).findAllByLastNameLike(anyString());
        inOrder.verify(model).addAttribute(anyString(), anyList());
    }