A general comment on "verifyDiffRejected": I've been disappointed sometimes by similarly negative tests (for the planner) that SEEM to be validating that queries in some subtle edge case get rejected, but in fact the queries just happened to be total garbage that no amount of planner improvement was going to help. Point being, it's nice to have some more specific assurance that things are getting rejected for the reason you expect -- is there any way to detect that in these tests -- test for a pattern in captured logging? Maybe when human readable diff is available, these same cases can be validated with a pattern match on that output.