@ManagedBean(name = "authBean")
@SessionScoped
public class AuthorizationBean implements Serializable{

    //Data access object for the users
    @Inject
    UserDao userDao;

    private User user; // The JPA entity.
    public User getUser() {
        if (user == null) {
            user = (User) FacesContext.getCurrentInstance().getExternalContext().getSessionMap().get("user");
            if (user == null) {
                Principal principal = FacesContext.getCurrentInstance().getExternalContext().getUserPrincipal();
                if (principal != null) {
                    user = userDao.findByEmail(principal.getName()); // Find User by j_username.
                }
            }
        }
        return user;
    }

    /**
     * Function that handles the logout
     * @return Redirect string that points to the login page
     */
    public String doLogout() {
        // invalidate the session, so that the session is removed
        FacesContext.getCurrentInstance().getExternalContext().invalidateSession();
        user = null;
        // return redirect to login page
        return "/login.xhtml?faces-redirect=true";
    }


}

@RunWith(PowerMockRunner.class)
@PrepareForTest(FacesContext.class)
public class AuthorizationBeanTest {

    private AuthorizationBean authorizationBean;

    @Mock
    User user;

    @Mock
    FacesContext facesContext;

    @Mock
    ExternalContext externalContext;

    @Before
    public void setUp() {
        authorizationBean = new AuthorizationBean();
        Map<String,Object> sessionMap = new HashMap<>();
        sessionMap.put("user", user);

        //Mocking the static function getCurrentInstance from FacesContext,
        //so a mocked user can be returned for the test
        PowerMockito.mockStatic(FacesContext.class);
        PowerMockito.when(FacesContext.getCurrentInstance()).thenReturn(facesContext);
        when(facesContext.getExternalContext()).thenReturn(externalContext);
        when(externalContext.getSessionMap()).thenReturn(sessionMap);
    }

    @Test
    public void doLogoutTest() throws NoSuchFieldException, IllegalAccessException {
        assertNotNull(authorizationBean.getUser());
        assertEquals("/login.xhtml?faces-redirect=true", authorizationBean.doLogout());

        //Check through reflection if the private field user is now null
        Field userField = authorizationBean.getClass().getDeclaredField("user");
        userField.setAccessible(true);
        User testUser = (User) userField.get(authorizationBean);
        assertNull(testUser);
    }

}

protected boolean isUserNull () {
    return user==null;
}

//Mocking the static function getCurrentInstance from FacesContext,
        //so a mocked user can be returned for the test
        PowerMockito.mockStatic(FacesContext.class);
        PowerMockito.when(FacesContext.getCurrentInstance()).thenReturn(facesContext);
        when(facesContext.getExternalContext()).thenReturn(externalContext);
        when(externalContext.getSessionMap()).thenReturn(sessionMap);

FacesContext.getCurrentInstance().getExternalContext().getSessionMap().get("user");

FacesContext.getCurrentInstance().getExternalContext().getUserPrincipal();

userDao.findByEmail(principal.getName());