The redesign effort (#3859) left behind only very minimal system tests. The older implementation had much broader system test coverage:

• Listing topics and subscriptions in the client's project.
• Creating subscriptions with non-default settings.
• Listing subscriptions bound to a topic.
• Setting / getting IAM policy for topics and subscriptions
• Creating / seeking snapshots.

I noticed the missing tests today when I went looking for examples of updating a topic's IAM policy.