SwingUtilities.invokeLater(() -> {
    JFrame mainWindow = new JFrame();
    mainWindow = new JFrame("MainFenster");
    mainWindow.setSize(500, 500);
    mainWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    mainWindow.setLocationRelativeTo(null);
    mainWindow.setLayout(new BorderLayout());
    LoginView loginView = new SwingLoginView(mainWindow);

    LoginModel loginModel = new LoginModelImpl();
    LoginService loginService = new LoginServiceImpl(loginModel);

    LoginPresenter presenter = new LoginPresenter(loginView, loginService);
    loginView.setPresenter(presenter);

    mainWindow.setVisible(true);

});

public interface View {
// Not sure what woudl go here, but just in case...
}

public interface LoginView extends View {

    void setErrorMessage(String errorMessage);

    void setNotificationMessage(String message);

    void navigateToHome(); // Should go here?

    void setPresenter(LoginPresenter presenter);

    interface LoginViewEventListener {
        void loginButtonClicked(String username, String password);
    }

}

public class SwingLoginView implements LoginView {

    private JFrame mainFrame;
    private LoginPresenter presenter;
    private JTextArea errorMessage;
    private JTextArea password;
    private JTextArea username;
    private JTextArea notificationMessage;
    private JPanel panel;

    public SwingLoginView(JFrame mainWindow) {
        this.mainFrame = mainWindow;
        inititialize();

    }

    private void inititialize() {

        initializeComponents();

    }

    private void initializeComponents() {
        errorMessage = new JTextArea();
        errorMessage.setText("Hello");

        notificationMessage = new JTextArea();
        notificationMessage.setText("UU");

        password = new JTextArea();
        password.setText("password");

        username = new JTextArea();
        username.setText("username");

        JButton loginButton = new JButton("Press");
        loginButton.addActionListener((e) -> {
            // Could validation go here?
            presenter.loginButtonClicked(username.getText(), password.getText());
        });
        panel = new JPanel();
        panel.add(loginButton);

        panel.add(errorMessage);
        panel.add(notificationMessage);
        panel.add(password);
        panel.add(username);
        mainFrame.add(panel, BorderLayout.NORTH);
    }

    @Override
    public void setErrorMessage(String errorMessage) {
        this.errorMessage.setText(errorMessage);
    }

    @Override
    public void setNotificationMessage(String message) {
        this.notificationMessage.setText(message);

    }

    @Override
    public void navigateToHome() {
        // TODO Auto-generated method stub

    }

    @Override
    public void setPresenter(LoginPresenter presenter) {
        this.presenter = presenter;

    }
}

public class LoginPresenter implements Presenter, LoginView.LoginViewEventListener {

private LoginView referenceToLoginView;
private LoginService referenceToLoginService;

public LoginPresenter(LoginView referenceToLoginView, LoginService loginService) {
    this.referenceToLoginView = referenceToLoginView;
    this.referenceToLoginService = loginService;
}

@Override
public void loginButtonClicked(String username, String password) {
    System.out.println("presenter called");

    if (username.equals("") || password.equals("")) {
        this.referenceToLoginView.setErrorMessage("Password and or username empty");
        return; // OK?
    }

    LoginModel loginModel = referenceToLoginService.login(username, password);

    referenceToLoginView.setNotificationMessage("NEU");

}

@Override
public View getView() {
    return referenceToLoginView;
}
}

@RunWith(MockitoJUnitRunner.class)
public class LoginTest {

    @Mock
    private LoginView mockLoginView;
    @Mock
    private LoginService mockLoginService;
    private LoginPresenter loginPresenter;

    @Before
    public void setUp() {
        loginPresenter = new LoginPresenter(mockLoginView, mockLoginService);
        mockLoginView.setPresenter(loginPresenter);
    }

    @Test
    public void loginShouldFailIfCredentialsAreEmpty() {
        loginPresenter.loginButtonClicked("", "");
        Mockito.verify(mockLoginView).setErrorMessage("Password and or username empty");
    }

}