ApplicationPresenter.java

public class ApplicationPresenter
        extends Presenter<ApplicationPresenter.MyView, ApplicationPresenter.MyProxy>
        implements ApplicationUiHandlers { // Added the UiHandlers
    interface MyView extends View, HasUiHandlers<ApplicationUiHandlers> {
        void displayUsername(String username);
    }
    
    // ...

    @Inject
    ApplicationPresenter(
            EventBus eventBus,
            MyView view,
            MyProxy proxy,
            UserService userService) {
        super(eventBus, view, proxy, RevealType.Root);

        this.userService = userService;

        getView().setUiHandlers(this); // <- This is also checked by a test.
    }

    @Override
    public void saveUsername(String username) {
        userService.saveUsername(username);

        String newName = userService.getUsername();
        getView().displayUsername(newName);
    }
    
    // ...
}

ApplicationPresenterTest.java

@RunWith(JukitoRunner.class)
public class ApplicationPresenterTest {
    // New tests
    @Test
    public void ctor_setsUiHandlers() {
        verify(view).setUiHandlers(same(presenter));
    }

    @Test
    public void saveUsername_delegatesToService() {
        presenter.saveUsername(A_USERNAME);

        verify(userService).saveUsername(A_USERNAME);
    }

    @Test
    public void saveUsername_displaysNewUsernameInView() {
        given(userService.getUsername()).willReturn(A_USERNAME);

        presenter.saveUsername(A_USERNAME);

        verify(view).displayUsername(A_USERNAME);
    }
}