`<errorCode>` is considered optional so I'd suggest to avoid rendering this element in the "right case" (i.e. 200). Otherwise, we don't need only changing this .test, but also the documentation in https://forge.fi-ware.eu/plugins/mediawiki/wiki/fiware/index.php/Publish/Subscribe_Broker_-_Orion_Context_Broker_-_User_and_Programmers_Guide#Context_availability_subscriptions.