deployment.sentry['foo/0'] returns an empty list if the foo/0 unit does not exist. The Cassandra tests stopped passing because it assumed the first unit in a deployed service would be cassandra/0, but that has changed with Juju 1.25 where unit numbers will not be reused if you destroy a service and create another with the same name.
Not quite.
deployment. sentry[ 'foo/0' ] returns an empty list if the foo/0 unit does not exist. The Cassandra tests stopped passing because it assumed the first unit in a deployed service would be cassandra/0, but that has changed with Juju 1.25 where unit numbers will not be reused if you destroy a service and create another with the same name.