Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add int2t05/engineering-skills --skill tddgit clone --depth 1 https://github.com/int2t05/engineering-skillsWrote 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/int2t05/engineering-skills/tdd)<a href="https://agentmods.dev/skills/int2t05/engineering-skills/tdd"><img src="https://agentmods.dev/badge/skills/int2t05/engineering-skills/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/int2t05/engineering-skills/tdd"><img src="https://agentmods.dev/badge/skills/int2t05/engineering-skills/tdd.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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 | $0.00027 | $0.00330 |
| Opus 5.5 | $0.00011 | $0.00132 |
| Sonnet 5.5 | $0.00005 | $0.00066 |
| Haiku 4.5 | $0.00003 | $0.00033 |
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 8d 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.
What it actually says
Test-Driven Development
When to use
- Implement behavior through a focused red-green-refactor loop.
Not for: implement for planned delivery; test-generation for existing behavior.
Steps
-
Find real commands, layout and public seam; use real code and controlled data, disclosing external substitutes.
-
Write one behavior test, run it and confirm failure from missing or incorrect behavior rather than harness errors.
-
Implement minimally, run the focused test and relevant regressions, and refactor while green.
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Repeat for the next behavior and finish relevant verification; report observed red/green evidence and commit only on request.
Verify
- A meaningful failure preceded the passing fix; assertions use independent expected behavior and checks are not disabled.
References
- engineering-principles.md — shared decision boundaries, scope and verification.
- references/test-strategy.md — test pyramid, test-double hierarchy (Real > Fake > Stub > Mock), DAMP over DRY
- references/testing-anti-patterns.md — mock misuse, test-only methods, partial mocks, gate functions
- references/mocking.md — when to mock, designing for mockability
- references/good-tests.md — good vs bad test examples, tautological tests
What ships with it
5 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.
- 8d ago Changed · -71 lines · -66 tokens per session 570a15917420
- 1mo ago First seen · 106 lines · 93 tokens per session scan A f95aea52dee9
tdd is a skill published in the GitHub repository int2t05/engineering-skills (3 stars, last pushed 9d ago), licensed MIT. It adds 27 tokens to every session and 330 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 2026-08-31.
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For a build brief, implementing a spec or tracked item, or mid-build discoveries tempting scope expansion, build thin verified slices with test-first checks at named boundaries, proportional validation elsewhere, and respect for scope and commit instructions.
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plan
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