def METHOD_NAME(self):
    # Issue 17198: check that ndbm which is referenced in whichdb is defined
    db_file = '{}_ndbm.db'.format(_fname)
    with open(db_file, 'w'):
        self.addCleanup(test.support.unlink, db_file)
    self.assertIsNone(self.dbm.whichdb(db_file[:-3]))