code: def testPackSize(self):
      for array, typecode in arrayimpl.loop():
          with arrayimpl.test(self):
              if typecode in self.skipdtype:
                  continue
              datatype = array.TypeMap[typecode]
              itemsize = datatype.Get_size()
              overhead = datatype.Pack_size(0, self.COMM)
              for count in range(10):
                  with self.subTest(count=count):
                      pack_size = datatype.Pack_size(count, self.COMM)
                      self.assertEqual(
                          pack_size - overhead, count * itemsize
                      )
  
file_path: mpi4py/test/test_pack.py
imports: from mpi4py import MPI
  import mpiunittest
  import arrayimpl
  import os
label_desc: Use image node_id 1 for calling the BaseTestPack obj's underlying member method code with example usage: obj.testPackSize() without return types