Grep won't find your dead gates. A fill-rate query will.

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: SELECT COUNT ( * ) AS total , SUM ( some_column IS NOT NULL ) AS filled FROM some_table ; If that comes back near 100%, this note may simply not apply to your codebase, and that's a real result, not a failure to reproduce it. Keep that in mind through the rest of this — every finding below is downstream of a query shaped like this one, not downstream of reading code and guessing. Grep is not the detector My first instinct, the same one the predecessor note's fixes point toward, was to grep for the failure shape — a default value, an unpopulated argument, a call site missing a keyword. In one afternoon it produced both a false positive and a false negative. The sharper miss: a literal grep for a write path failed to find an INSERT OR REPLACE statement that was, in fact, live and doing exactly the writing I was looking for. Grep matched the shape of the bug I expected walking in, not the shape the code actually had. Everything that survived scrutiny below came from asking a database a question, not from asking a shell how a string was spelled. The question that works is: of all the rows that exist, how many have this column fi