Artifact: Refusing an Unverifiable Change Until a Test Exists
A proposed change to a module with zero test coverage, refused until a test exists to verify it -- exercises co-22, co-13.
[Agent]: Proposes a diff to legacy/pricing_calendar.py, changing how holiday
surcharges are computed for the December calendar.
[Reviewer check]: grep -rl "pricing_calendar" tests/
-> (no output -- zero existing tests cover this module)
[Refusal, as written down]: "Refusing this diff. legacy/pricing_calendar.py has
no test coverage at all, and December holiday-surcharge logic is exactly the
kind of case-heavy code that LOOKS right on read-through but is easy to get
subtly wrong. There is no accompanying verification path -- I can confirm this
diff is plausible, not that it is correct. No merge until a test exists."
[Agent, second pass]: writes a characterization test first, pinning today's
actual (pre-diff) December-surcharge output for five known dates.
[Test run against pre-diff code]: pytest tests/test_pricing_calendar.py -q
-> 5 passed (the characterization test matches CURRENT behavior)
[Diff re-applied, characterization values updated to the intended new
surcharges, delta reviewed line by line, test rerun]:
pytest tests/test_pricing_calendar.py -q -> 5 passed
[MERGED] -- only after tests/test_pricing_calendar.py existed and passed
against the diff.The refusal did not block the change forever -- it blocked it until a verification path existed. Writing the characterization test first (pinning the current, pre-diff behavior) gave the reviewer something concrete to diff the intended change against, rather than relying on a read-through alone for case-heavy calendar logic.
Verify: the transcript shows an explicit refusal citing the absence of any test, followed only
later by a merge that happens strictly after tests/test_pricing_calendar.py exists and passes --
satisfying ex-43's rule that no diff merges without an accompanying verification path.
Last updated July 17, 2026