| name | demo-2-bug-hunt |
| description | Demo skill that hunts two seeded bugs in a tiny stats package until its tests go green, then files a detective-style CASE_FILE.md with the evidence. |
Play detective on a small statistics package: reproduce the failures, hunt down the bugs, fix
them until every test passes, and file a case report.
Setup
- Copy the seeded project into a working directory you own (fresh — delete a stale one first):
rm -rf .decode/outputs/bug-hunt && mkdir -p .decode/outputs && cp -r .decode/skills/demo-2-bug-hunt/references/buggy_repo .decode/outputs/bug-hunt
- Change into it and run the suite to see the failures:
cd .decode/outputs/bug-hunt/ && uv run pytest -q
- Save the crime scene: keep the exact failing-test output — the failure names and the
expected-vs-actual values — you will quote it in the case file at the end.
Exactly two tests fail as committed — one in median, one in variance. Do NOT edit the tests;
they encode the correct behaviour. Fix stats.py instead.
Hunt
Track the investigation with todo_write (reproduce → suspect A → suspect B → verify → case
file) and tick items off as you close them.
- Read
test_stats.py to learn the contract each failing test asserts (the expected values are
the spec).
- Read
stats.py and locate the defect behind each failure with grep/read. The LSP
diagnostics that surface on your edits will help you catch typos and type slips as you go.
- There are two independent bugs:
median returns the wrong element for odd-length inputs (an indexing off-by-one).variance comes back with the wrong sign (it should never be negative).
Fix and verify
- Fix the root cause of each bug in
stats.py — the smallest correct change, not a special case
that only satisfies the one test input.
- Re-run
uv run pytest -q and confirm the whole suite is green. Keep that green one-liner too.
File the case report
Write .decode/outputs/bug-hunt/CASE_FILE.md — short, punchy, detective-flavoured:
- The symptoms — the failing test names and the quoted expected-vs-actual output from setup
step 3.
- The culprits — one section per bug: the guilty line (
stats.py:<line>), the root cause in
one sentence, and the before/after of the fixed line.
- Case closed — the quoted green
pytest -q summary line proving the suite passes.
Report the two root causes, the one-line fix for each, and point the human at CASE_FILE.md.
