We're shipping a 30-product pipeline at our agency. This is product #22: a Junk Removal Business Starter Kit — a pricing calculator plus operations docs for people starting a hauling business. It's 18 plain files: 13 Markdown docs, 3 CSVs, a LICENSE, and one Python script. It sells on Gumroad at a $1 intro price.
None of that is the interesting part. The interesting part is that a folder of documents got treated like code: it has a quality gate.
The product is data, so we test it like data
Every number in the kit — the six worked quotes, the startup-cost totals — is derived from the shipped CSVs. Nothing is hand-typed into the prose. So the real question was: what happens when a rate card cell drifts and nobody notices?
self_qos.py answers it. It's stdlib-only Python, no dependencies, and it:
- Re-derives all six worked quotes from the rate card CSV
- Re-sums the startup-cost totals three independent ways
- Prints five PASS lines when everything agrees
- Exits 1 with a plain message — no traceback — on malformed input
The malformed path isn't theoretical. We drilled it with seven edge cases: empty files, missing columns, non-numeric weights, negative prices. Every one exits cleanly with a message instead of a stack dump. Output shape:
$ python3 self_qos.py
PASS quotes: 6/6 re-derived from rate card
PASS startup totals: 3/3 methods agree
PASS edge drills: 7/7 malformed inputs exit 1 cleanly
PASS no-traceback: stderr is a message, not a stack dump
PASS self_qos: all checks green
The mutation drill: plant a bug, watch it get caught
Run by a separate process, the gate reports 59/59 checks PASS. Then the part we liked most: a mutation drill. We planted a one-cent error in a worked quote — $654.01 instead of $654.00 — and re-ran the verifier. It failed, and it named the exact quote that was wrong.
That's the whole argument for cheap consistency tests. A one-cent discrepancy in a pricing document is invisible to a human skimming 13 Markdown files. It's trivial to catch when you re-derive the number from the CSV the buyer actually receives.
Honest limits
- The prices are example figures — verify them locally before you quote anyone.
- No income claims anywhere. We don't promise what a hauling business will earn.
- Personal-use license: you can use the kit, you can't resell the files.
- Dump and transfer-station rates vary by region, so your cost per load will differ.
The link
Full disclosure — we built and sell this kit: https://nandminc.gumroad.com/l/junk-removal-kit
What surprised us
The verifier took less time to write than one of the operations docs. The expensive part was never the test — it was deciding what "correct" means for a quote: which line items, which minimum load fee, which rounding rule. Once that was written down as CSV data, checking it became mechanical.
So if you're shipping documents, spreadsheets, templates — anything where the value is in the numbers — give the artifact a recompute step. Five PASS lines and a planted one-cent bug caught by name will tell you more than a reread ever will.
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