code: def test_readonly_files(self):
      with os_helper.temp_dir() as dir:
          fname = os.path.join(dir, "db")
          with dumbdbm.open(fname, "n") as f:
              self.assertEqual(list(f.keys()), [])
              for key in self._dict:
                  f[key] = self._dict[key]
          os.chmod(fname + ".dir", stat.S_IRUSR)
          os.chmod(fname + ".dat", stat.S_IRUSR)
          os.chmod(dir, stat.S_IRUSR | stat.S_IXUSR)
          with dumbdbm.open(fname, "r") as f:
              self.assertEqual(sorted(f.keys()), sorted(self._dict))
              f.close()
  
imports: import contextlib
  import io
  import operator
  import os
  import stat
  import unittest
  import dbm.dumb
  from test import support
  from test.support import os_helper
  from functools import partial
label_desc: Use image node_id 23 for calling the DumbDBMTestCase obj's underlying member method code with example usage: obj.test_readonly_files() without return types