def test_optional_pre(self):
        del self.good_config['endpoints']['POST /*/containers/create']['pre']
        self.config._parse_adapters(self.good_config)
        endpoint_config = self.config.endpoint("POST /*/containers/create")
        self.assertEquals(endpoint_config.pre, [])
``pre`` is an optional configuration key.
dataset/ETHPy150Open ClusterHQ/powerstrip/powerstrip/test/test_config.py/ConfigurationValidationTests.test_optional_pre