assertNull(user.getMail());

        user.setMail("******@****.***");
        assertEquals("******@****.***", user.getMail());
    }

    @Test
    public void test_user_telephoneNumber() {
        final User user = new User();
        assertNull(user.getTelephoneNumber());

        user.setTelephoneNumber("123-456-7890");
        assertEquals("123-456-7890", user.getTelephoneNumber());