def METHOD_NAME(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()