One of the things that surprised me about this analysis was just how many bugs we found that had to do with the actual Raft implementation. Usually when I test Raft-based systems the bugs are at the edges--like the coupling of the system to the Raft library, treating it like an externally-queryable log rather than the driver of a state machine, and so on. We found integration bugs here too, but also a fair number of issues in the Raft library itself--and this is despite Redis-Raft having existing integration tests!
This stuff is hard!