code: def test_empty_value(self):
      if dbm.ndbm.library == "Berkeley DB":
          self.skipTest(
              "Berkeley DB doesn't distinguish the empty value "
              "from the absent one"
          )
      self.d = dbm.ndbm.open(self.filename, "c")
      self.assertEqual(self.d.keys(), [])
      self.d["empty"] = ""
      self.assertEqual(self.d.keys(), [b"empty"])
      self.assertIn(b"empty", self.d)
      self.assertEqual(self.d[b"empty"], b"")
      self.assertEqual(self.d.get(b"empty"), b"")
      self.assertEqual(self.d.setdefault(b"empty"), b"")
      self.d.close()
  
imports: from test.support import import_helper
  from test.support import os_helper
  import os
  import unittest
  import dbm.ndbm
  from dbm.ndbm import error
label_desc: Use image node_id 4 for calling the DbmTestCase obj's underlying member method code with example usage: obj.test_empty_value() without return types