}

  @Test
  public void forGraph_depthFirstPreOrder_tree() throws Exception {
    Traverser<Character> traverser = Traverser.forGraph(TREE);

    assertEqualCharNodes(traverser.depthFirstPreOrder('h'), "hdabcegf");
    assertEqualCharNodes(traverser.depthFirstPreOrder('d'), "dabc");
    assertEqualCharNodes(traverser.depthFirstPreOrder('a'), "a");
  }

  @Test