code: def testPackSize(self):
      for array, typecode in arrayimpl.loop():
          with arrayimpl.test(self):
              if typecode in self.skipdtype:
                  continue
              datatype = array.TypeMap[typecode]
              overhead = datatype.Pack_external_size(EXT32, 0)
              for count in range(10):
                  with self.subTest(count=count):
                      pack_size = datatype.Pack_external_size(
                          EXT32, count
                      )
                      real_size = pack_size - overhead
                      self.assertGreaterEqual(real_size, 0)
  
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 BaseTestPackExternal obj's underlying member method code with example usage: obj.testPackSize() without return types