It is not clear that pjdfstest establishes full POSIX semantic compliance. After a short search of the repo I did not see anything that exercises multiple unrelated processes atomically writing with O_APPEND, for example. And the fact that their graphic shows applications interfacing with JuiceFS over NFS and SMB casts further doubt, since both of those lack many POSIX semantic properties.

Over the decades I have written test harnesses for many distributed filesystems and the only one that seemed to actually offer POSIX semantics was LustreFS, which, for related reasons, is also an operability nightmare.