Originally published on hexisteme notes.
A predecessor note diagnosed three production features that passed every dedicated unit test and never executed at all, and why a unit test structurally can't see that gap.
That note answered three cases I already knew about, because I'd already tripped over them. It didn't answer the question that matters once you've found three: how do you find the rest — the ones nobody happened to notice yet? This is that search: the tool that actually works, what it found across seven projects, and a fourth failure shape that the predecessor note's two fixes don't reach at all, because in that fourth shape the code was never the thing that was broken.
The query, before the argument
Before any of the specifics, here is the shape of the query, so you can run something like it against your own tables in under a minute:
