code: def test_nN_code(self):
      # n and N don't exist in standard sizes
      def assertStructError(func, *args, **kwargs):
          with self.assertRaises(struct.error) as cm:
              func(*args, **kwargs)
          self.assertIn("bad char in struct format", str(cm.exception))
  
      for code in "nN":
          for byteorder in ("=", "<", ">", "!"):
              format = byteorder + code
              assertStructError(struct.calcsize, format)
              assertStructError(struct.pack, format, 0)
              assertStructError(struct.unpack, format, b"")
  
imports: from collections import abc
  import array
  import gc
  import math
  import operator
  import unittest
  import struct
  import sys
  import weakref
  from test import support
  from test.support import import_helper
  from test.support.script_helper import assert_python_ok
label_desc: Use image node_id 7 for calling the StructTest obj's underlying member method code with example usage: obj.test_nN_code() without return types