code: def test_apply(self):
      papply = self.pool.apply
      self.assertEqual(papply(sqr, (5,)), sqr(5))
      self.assertEqual(papply(sqr, (), {"x": 3}), sqr(x=3))
  
imports: from mpi4py import MPI
  import mpi4py.util.pool
  import concurrent.futures
  import itertools
  import functools
  import warnings
  import unittest
  import time
  import sys
  import os
label_desc: Use image node_id 4 for calling the BaseTestPool obj's underlying member method code with example usage: obj.test_apply() without return types