Borrowing it
Nothing to install: this file belongs to ahonn/dotfiles. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/ahonn/dotfiles/master/.claude/skills/tdd/SKILL.mdgit clone --depth 1 https://github.com/ahonn/dotfilesWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/ahonn/dotfiles/tdd)<a href="https://agentmods.dev/skills/ahonn/dotfiles/tdd"><img src="https://agentmods.dev/badge/skills/ahonn/dotfiles/tdd/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/ahonn/dotfiles/tdd"><img src="https://agentmods.dev/badge/skills/ahonn/dotfiles/tdd.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00024 | $0.00477 |
| Opus 5.5 | $0.00010 | $0.00191 |
| Sonnet 5.5 | $0.00005 | $0.00095 |
| Haiku 4.5 | $0.00002 | $0.00048 |
Grade A, and why
tdd scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 20d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 36 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-Driven Development
Use this workflow only for test mode tdd or an explicit test-first request. The applicable AGENTS.md testing policy owns mode selection; this skill does not turn skip, verify-only, or add-tests into TDD.
Establish the boundary
Inspect the implementation, nearby tests, and the relevant interface before the first test. Read domain documentation only when it resolves uncertainty about the behavior or vocabulary under test.
- Use the existing test harness for this surface. If none exists, follow the task's scope and testing policy; introduce one only when the request supports it.
- Choose the smallest public boundary that exposes the required behavior. State the boundary in the plan when useful; routine test placement does not require user confirmation.
- Ask only when an unresolved behavior or interface decision materially changes scope or risk. Continue independent work while that decision is pending.
Work in vertical slices
- Select one observable behavior from the requirement or reproduced bug.
- Write a focused test and run it. Confirm it fails for the missing behavior, not a broken fixture, import, or environment.
- Add the implementation needed for that behavior and run the relevant test again.
- Refactor when it improves the changed code, keeping the relevant tests green. A separate review skill is not a prerequisite.
- Repeat for the next meaningful behavior. Finish with the checks appropriate to the changed surface and report only checks actually run.
Do not write a batch of speculative tests before implementing any behavior. Let each completed slice inform the next one.
Keep tests worth maintaining
- Verify behavior through public interfaces, with expected results drawn from a requirement, worked example, or other independent source of truth.
- Avoid private-method assertions and internal call-order checks unless that interaction is itself the contract.
- Prefer real collaborators where practical. Isolate external boundaries when needed for reliable, focused tests.
- Cover meaningful failure paths and regressions without mirroring the implementation or adding cases solely to increase coverage.
What ships with it
3 files beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 20d ago Changed · -13 lines · -95 tokens per session 2b283edf7c92
- 1mo ago First seen · 49 lines · 119 tokens per session scan A fae7ff3f767c
tdd is a skill published in the GitHub repository ahonn/dotfiles (63 stars, last pushed 6d ago), licensed MIT. It adds 24 tokens to every session and 477 once invoked, about $0.0001 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.
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