@TestOnly
  public void cleanPersistedContents() {
    IntArrayList ids = new IntArrayList(vfsPeer.listRoots());
    while (!ids.isEmpty()) {
      int id = ids.popInt();
      if (isDirectory(getFileAttributes(id))) {
        int[] children = vfsPeer.listIds(id);
        ids.addElements(ids.size(), children, 0, children.length);
      }
      else {
        doCleanPersistedContent(id);
      }
    }
  }
@TestOnly
  public void cleanPersistedContents()