assertEqualCharNodes(traverser.breadthFirst(charactersOf("bg")), "bgcdh");
    assertEqualCharNodes(traverser.breadthFirst(charactersOf("ga")), "gahbcd");
  }

  @Test
  public void forTree_breadthFirst_twoTrees() {
    Iterable<Character> result = Traverser.forTree(TWO_TREES).breadthFirst('a');

    assertEqualCharNodes(result, "ab");
  }

  @Test
  public void forTree_breadthFirstIterable_twoTrees() {