public void testUpdate() {
TreeLeaf3D leaf3D = leaf.getTreeLeaf3D();
// the leaf should be a subscriber of the leaf3D
assertEquals(1, leaf3D.countSubscribers());
// assert the leaf is really one of the subscribers of the leaf3D
leaf3D.deleteSubscriber(leaf);
assertEquals(0, leaf3D.countSubscribers());
publisherHelper.addSubscriberTo(leaf);