'Adding/Deleting the last post in a thread should
update the last_post field'

def test_last_post_updated(self):

    t = ThreadFactory()
    u = UserFactory()
    new_post = t.new_post(creator=u, content='test')
    eq_(t.last_post.id, new_post.id)
    new_post.delete()
    self.assertIsNone(t.last_post.id)
