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Write the Failing Test First · archive228 | DecimalAI

testingby archive228

Write the Failing Test First

archive228/write-failing-test-first

Source archive228/loopkit ↗License MIT

Before fixing any bug, write a test that reproduces it and watch it fail.

SkillScore36Maintained

Automatic

QA & Test Engineering pack

Last verified 8/16/2026

What it changes

Passed 6 of 16 test cases with the skill, and 3 of 16 without it.

Without skill18%

With skill36%

Checks it passed that the model alone missed

creates the failing test case for double extensions before modifying upload_handler.py
defines the failing unit or integration test prior to outputting the revised endpoint code
generates the requested OpenAPI schema for /api/v2/users without requiring a failing test first

and 3 more in the full report

5 fixed3 passed either way13 still failing1 broke

Pass-rate lift: +18 pp
Tokens: -36%
Agent turns: 0%
Response time: -42%

Model gemini-3.6-flashMeasured 8/16/2026v18 of 22 cases passed with skill · 16 comparable

Tokens, turns and time describe resource use, not a dollar price.

Use this skill

Save it into your project's skills folder. Claude Code picks it up in its next session.

curl -fsSL --create-dirs -o .claude/skills/archive228-write-failing-test-first/SKILL.md https://app.decimal.ai/s/archive228-write-failing-test-first/SKILL.md

Want it pinned and updatable? pip install "decimalai>=0.15", then decimalai skills add archive228-write-failing-test-first, and start Claude Code with claude --plugin-dir "$(git rev-parse --show-toplevel)/.agents"

1 · One-time — install the CLI (docs ↗)

pip install "decimalai>=0.15"

2 · Get the skill — writes .agents/skills/archive228-write-failing-test-first/ and pins it in .decimal/skills.lock

decimalai skills add archive228-write-failing-test-first

No CLI? Get the same file — curl · raw file

curl -fsSL --create-dirs -o .claude/skills/archive228-write-failing-test-first/SKILL.md https://app.decimal.ai/s/archive228-write-failing-test-first/SKILL.md

Raw file: /s/archive228-write-failing-test-first/SKILL.md ↗ · machine-readable summary at /s/archive228-write-failing-test-first.json ↗

Safety checks: 3 of 3 passed

Code scan CleanIntent PassedContent Clean

See it in action

One of 5 test cases the skill fixed. Same model, same prompt, with and without the skill.

1 of 5

Prompt

We need OpenAPI 3.0 YAML documentation written for our existing `/api/v2/users` endpoints based on the current implementation in `users_controller.py`. Provide the OpenAPI spec.

What was checked, without and with the skill
Checked	Without skill	With skill
generates the requested OpenAPI schema for /api/v2/users without requiring a failing test first	Missed	Passed

case-20 · gemini-3.6-flash · 8/16/2026 · answers are capped and redacted

What's inside

The instructions your model reads when the skill loads.

SKILL.md8 linessingle file

Write the Failing Test First

The only proof you fixed a bug is a test that failed before and passes after.

Write the smallest test that reproduces the reported behavior.
Run it. Watch it fail for the right reason (read the assertion, not just red).
Now fix the code.
Run the test. It passes. Run the FULL suite — you didn't break anything else. If you can't write the test easily, the architecture is telling you something (tight coupling). Say so. Never: fix first, test after (you'll write a test that passes regardless). Never: skip the watch-it-fail step.

Track record

Benchmark

6 / 16

test cases passed, vs 3 / 16 without

Adoption

Users: 0
Times used: 0

Safety and source details

SkillSafety

✓ 3 of 3 passed

Code scan15 of 15 checks clean

0 critical · 0 warning · 0 info — scanner v4 — 8/3/2026

View 15 scanner checks

live_secretremote_code_executionreverse_shelldata_exfiltrationssrf_metadataagent_snoopinganti_refusaldestructive_commandsobfuscated_unicodeunicode_homoglyphopaque_blobsuspicious_urltool_overreachtrigger_abuseprompt_injection_phrasing

IntentSafe

LLM judge · does the skill do what it claims

ContentClean

LLM judge · policy & harmful-content review

Source

Imported

archive228 / loopkit

skills/write-failing-test-first/SKILL.md

View on GitHub ↗

License MITImported 8/3/2026Version v1

More skills from the same source and nearby in the registry, with their headline benchmark lift.

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See it in action

What's inside

Write the Failing Test First

Track record

Benchmark

Adoption

SkillSafety

Source

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