code: def test_context_manager(self):
      with gdbm.open(filename, "c") as db:
          db["gdbm context manager"] = "context manager"
  
      with gdbm.open(filename, "r") as db:
          self.assertEqual(list(db.keys()), [b"gdbm context manager"])
  
      with self.assertRaises(gdbm.error) as cm:
          db.keys()
      self.assertEqual(
          str(cm.exception), "GDBM object has already been closed"
      )
  
imports: from test import support
  from test.support import import_helper, cpython_only
  import unittest
  import os
  from test.support.os_helper import TESTFN, TESTFN_NONASCII, unlink, FakePath
label_desc: Use image node_id 9 for calling the TestGdbm obj's underlying member method code with example usage: obj.test_context_manager() without return types