code: def _empty_mapping(self):
      self.counter += 1
      x = shelve.open(self.base_path + str(self.counter), **self._args)
      self.addCleanup(x.close)
      return x
  
imports: import unittest
  import dbm
  import shelve
  import pickle
  import os
  from test.support import os_helper
  from collections.abc import MutableMapping
  from test.test_dbm import dbm_iterator
  from test import mapping_tests
label_desc: Use image node_id 1 for calling the TestShelveFileBase obj's underlying member method code with example usage: obj._empty_mapping() and returns: x