Test when the client explicitly asks (via horizonName) for something in the configuration.
Test when the client implicitly asks for something (via simulatedSniName or real SNI name) not in the configuration that the server replies with a valid isMaster response which appears as-if no horizon feature were present.
Test when the client implicitly asks for a horizon (via appName) not in the configuration that the server replies with a valid isMaster response which appears as-if no horizon feature were present.
Test when the client explicitly asks for something not in the configuration that an error is reported in the isMaster response.