Path dir = fs.getPath("dir");
        assertEquals(6, MoreFiles.listFiles(dir).size());

        method.delete(dir);
        method.assertDeleteSucceeded(dir);

        assertEquals(
            "contents of /dontdelete deleted by delete method " + method,
            3,
            MoreFiles.listFiles(fs.getPath("/dontdelete")).size());
      }
    }
  }

        @Override
        public Iterable<File> successors(File file) {
          // check isDirectory() just because it may be faster than listFiles() on a non-directory
          if (file.isDirectory()) {
            File[] files = file.listFiles();
            if (files != null) {
              return Collections.unmodifiableList(Arrays.asList(files));
            }
          }