assertEqualCharNodes(traverser.breadthFirst(charactersOf("gd")), "gdfabc");
    assertEqualCharNodes(traverser.breadthFirst(charactersOf("bdgh")), "bdghacfe");
  }

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

    assertEqualCharNodes(result, "ab");
  }

  @Test
  public void forGraph_breadthFirstIterable_twoTrees() {