File dir2 = newDir("dir-2");

    assertThat(Files.fileTraverser().breadthFirst(rootDir))
        .containsExactly(rootDir, fileA, fileB, dir1, dir2);
  }

  public void testFileTraverser_multipleDirectoryLayers_breadthFirstStartsWithTopLayer()
      throws Exception {
    File fileA = newFile("file-a");
    File dir1 = newDir("dir-1");
    newFile("dir-1/file-b");
    newFile("dir-1/dir-2");