I’ve idly toyed with this problem as well, I think there’s a good opportunity to build a nice framework in Python with monkeypatching (or perhaps in other languages using DB/ORM middleware) so you don’t need to modify the code under test.

I think you can do better than explicit barrier() calls. My hunch is the test middleware layer can intercept calls and impose a deterministic ordering.

(There are a few papers around looking into more complex OS level frameworks to systematically search for concurrency bugs, but these would be tough to drop into the average web app.)