def tearDownClass(self):
        if 'KEEP_DATA' in os.environ:
            print("\nkeeping test database: %r." % self.db.db_name, file=sys.stderr)
        else:
            self.db.delete_all()
            self.runner.teardown_databases(self.old_config)
            django.test.utils.teardown_test_environment()
        super().tearDownClass()