code: private int initFileDirTables() {
      try {
        initFileDirTables(root);
      } catch (IOException e) {
        System.err.println(e.getLocalizedMessage());
        e.printStackTrace();
        return -1;
      }
      if (dirs.isEmpty()) {
        System.err.println("The test space " + root + " is empty");
        return -1;
      }
      if (files.isEmpty()) {
        System.err.println("The test space " + root +
            " does not have any file");
        return -1;
      }
      return 0;
    }
docs: Create a table that contains all directories under root and
  another table that contains all files under root.