Traverser<Character> traverser = Traverser.forTree(CYCLIC_GRAPH_CONTAINING_TREE);

    assertEqualCharNodes(traverser.depthFirstPostOrder('a'), "cdba");
    assertEqualCharNodes(traverser.depthFirstPostOrder('b'), "cdb");
    assertEqualCharNodes(traverser.depthFirstPostOrder('d'), "d");
  }

  @Test
  public void forTree_depthFirstPostOrderIterable_cyclicGraphContainingTree() throws Exception {