public void forTree_breadthFirstIterable_twoTrees() {
    assertEqualCharNodes(Traverser.forTree(TWO_TREES).breadthFirst(charactersOf("a")), "ab");
    assertEqualCharNodes(Traverser.forTree(TWO_TREES).breadthFirst(charactersOf("ca")), "cadb");
  }

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

    assertEqualCharNodes(result, "a");
  }

  public void forTree_breadthFirstIterable_twoTrees() {
    assertEqualCharNodes(Traverser.forTree(TWO_TREES).breadthFirst(charactersOf("a")), "ab");
    assertEqualCharNodes(Traverser.forTree(TWO_TREES).breadthFirst(charactersOf("ca")), "cadb");
  }

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

    assertEqualCharNodes(result, "a");
  }

   * "/home/alice", ...]}
   *
   * @since 23.5
   */
  public static Traverser<File> fileTraverser() {
    return Traverser.forTree(FILE_TREE);
  }

  private static final SuccessorsFunction<File> FILE_TREE =
      file -> {
        // check isDirectory() just because it may be faster than listFiles() on a non-directory

   * "/home/alice", ...]}
   *
   * @since 23.5
   */
  public static Traverser<File> fileTraverser() {
    return Traverser.forTree(FILE_TREE);
  }

  private static final SuccessorsFunction<File> FILE_TREE =
      file -> {
        // check isDirectory() just because it may be faster than listFiles() on a non-directory