Didn't fully understand the logic in the fake db but maybe I've misunderstood what we're trying to do there, also had some questions about the query. In general code looks good.

Ok, after your explanations Bruno and looking at this again, query and database fake implementation looks fine (except fake was missing one thing, see suggestion).

It'd be nice if you could do the remaining errors => xerrors and error block changes, but otherwise looks great. 👍🏻