@Override
   public void deleteOnExit() {
      // there exists no pre-CacheShutdown event, so unable to remove the entry
      throw new UnsupportedOperationException("Not implemented");
   }
@Test(expectedExceptions = UnsupportedOperationException.class)
   public void testDeleteOnExit() {
      fs.getFile("nonsuch.txt").deleteOnExit();
   }