@Test
public void testWalker() {

  AssociationWalker twalker = new AssociationWalker(at_descendant_of, rt_descendant, rt_ancestor);
  Set ancestors = twalker.walkTopics(bart);
  Assert.assertTrue("Expecting 2 members of association set. Got: " + String.valueOf(ancestors.size()),
         ancestors.size() == 2);
}