Spring Hibernate Dao - Testing the throwing of a constraint violation exception

[stephaneeybert]

I am coding a simple web application that uses Hibernate.

I would like to implement the following use case. The user tries to delete an entity, but this entity is being referenced by another one. So the user is presented with a message that explains that the entity cannot be deleted because it is being used by another one, and that the other entity should be deleted first.

I therefore would like to have a unit test against the Dao, that will ensure a constraint violation exception is thrown following a use case in which the user attempts to delete an entity referenced by another one.

I have several questions.

Question 1
----------

Is this unit test a good idea ?

Question 2
----------

How to "recover" from the exception, be it a checked application exception, or a Spring DataAccessException, or an HibernateException ?
That is, how to make use of the dao object after the catching of the exception ? And how to handle the entity object ?
I was told that the transaction should be rolled back, the session should be closed, and the entity object should be re-attached to a new session. This is a lot of action, and I have no idea how to implement it.

  @Test
  public void testDelete() {
    contactReferer0 = contactRefererDao.makePersistent(contactReferer0);
    contactReferer1 = contactRefererDao.makePersistent(contactReferer1);
    long count = contactRefererDao.countAllRows();
    assertEquals(2, count);
    contactRefererDao.makeTransient(contactReferer0);
    count = contactRefererDao.countAllRows();
    assertEquals(1, count);
    Contact contact = new Contact();
    contact.setEmail("email");
    contact.setMessage("message");
    DateTime contactDateTime = new DateTime();
    contact.setContactDateTime(contactDateTime);
    contact.setContactReferer(contactReferer1);
    contact = contactDao.makePersistent(contact);
    try {
      contactRefererDao.makeTransient(contactReferer1);
      fail(); // Assertion error !!! <<================================
    } catch (HibernateException e) {
    }
    count = contactRefererDao.countAllRows();
    assertEquals(1, count);
    contact.setContactReferer(null);
    contactRefererDao.makeTransient(contactReferer1);
    count = contactRefererDao.countAllRows();
    assertEquals(0, count);
  }

Thanks for any guidance on this.