@Test(expected = RuntimeException.class)
public void addTopMessageWithNullMessage() {

    Forum realForum = new ForumImpl();
    Identity initiatorIdentity = mock(Identity.class);
    Message firstMessage = null;
    publishEventTO = createPublishEventTO(initiatorIdentity);
    forumService.addTopMessage(realForum, firstMessage, initiatorIdentity, publishEventTO);
}