assertEqualCharNodes(traverser.depthFirstPreOrder(charactersOf("acdb")), "abdc");
    assertEqualCharNodes(traverser.depthFirstPreOrder(charactersOf("db")), "db");
  }

  @Test
  public void forGraph_depthFirstPreOrder_multigraph() {
    Traverser<Character> traverser = Traverser.forGraph(MULTI_GRAPH);
    assertEqualCharNodes(traverser.depthFirstPreOrder('a'), "abdc");
    assertEqualCharNodes(traverser.depthFirstPreOrder('b'), "bd");