code: def testGather(self):
      size = self.COMM.Get_size()
      rank = self.COMM.Get_rank()
      for smess in messages + [messages]:
          for root in range(size):
              rmess = self.COMM.gather(smess, root=root)
              if rank == root:
                  self.assertEqual(rmess, [smess] * size)
              else:
                  self.assertIsNone(rmess)
  
imports: from mpi4py import MPI
  import mpiunittest
  from functools import reduce
label_desc: Use image node_id 3 for calling the BaseTestCCOObj obj's underlying member method code with example usage: obj.testGather() without return types