Its a simple check to ensure `set_security_descriptor` and `get_security_descriptor` roundtrips properly.

We're assigning a group and user of `sids[:guest]` + adding 2 extra allow ACEs to the DACL.  While it's important to preserve the 2 extra ACEs, I think it's more important as a whole to preserve that our code roundtripped, which means verifying all the ACEs (and the ordering for that matter).  Again, this may already be expressed in another test that I might have missed.