I can't speak to "exhaustive", but Redis-Raft did have an extant unit and integration test suite prior to our collaboration. Here's what they looked like: https://github.com/RedisLabs/redisraft/tree/ff9fb28c74db880c...
I'm hesitant to draw too strong a conclusion here, and I can't speak for the Redis Labs team, but I do suspect that this is somewhere where... having an outside tester, like Jepsen (or a suitably adversarial QA team) can help detect missing-stairs sorts of problems. Coming from the perspective of a prospective operator (and having some experience with testing distributed systems), I immediately said "of course I want proxy mode by default", when this wasn't how the Redis-Raft designers necessarily intended things to be used--they intended smart clients to make it so that users wouldn't actually need proxy mode, so they hadn't focused on testing it that way.