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 personamanagmentlayer/pcl --skill tdd-workflowgit clone --depth 1 https://github.com/personamanagmentlayer/pclWrote 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/personamanagmentlayer/pcl/tdd-workflow)<a href="https://agentmods.dev/skills/personamanagmentlayer/pcl/tdd-workflow"><img src="https://agentmods.dev/badge/skills/personamanagmentlayer/pcl/tdd-workflow.svg" alt="Measured on agentmods" 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 | $0.00097 | $0.02006 |
| Opus 5 | $0.00048 | $0.01003 |
| Sonnet 5 | $0.00019 | $0.00401 |
| Haiku 4.5 | $0.00010 | $0.00201 |
Grade A, and why
tdd-workflow 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 2d 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 — 237 lines — stays where its author put it; the contents beside it link to each section on GitHub.
TDD Workflow
A procedure, not a body of knowledge. Follow the loop step by step; the value of TDD comes from the discipline of the sequence, not from knowing what it is.
When to Use This Skill
- The user asks for TDD, test-driven development, or "tests first"
- New behaviour is being added to code that already has a test suite
- A bug has been reported and the fix should not regress
- Existing code must be changed but has no tests to protect it
- The user wants confidence that a refactor preserved behaviour
Do not use this loop for exploratory spikes meant to be thrown away, or for code whose correct behaviour is not yet known. Explore first, then restart the loop against what you learned.
Core Concepts
The Loop
One cycle, three states, in this order and no other:
- Red — write one failing test that states the next increment of desired behaviour. Run it. Confirm it fails, and fails for the reason you expect.
- Green — write the simplest change that makes it pass. Not the best change; the simplest. Run the whole suite.
- Refactor — improve the code and the test with the suite green. Run after every structural change. Never change behaviour here.
The cycle is short by design: minutes, not hours. A long cycle means the increment was too large — shrink it.
Why Red Must Be Observed
A test that has never failed proves nothing. It may assert a tautology, target the wrong unit, or be silently skipped. Watching it fail, and reading the failure message, is the only evidence that the test is connected to the behaviour you intend to build.
The Increment
Each cycle should encode exactly one decision: one branch, one validation, one edge case. If you cannot state the next test in a sentence, the increment is too big.
Characterisation Tests
For untested legacy code, invert the loop. You do not know the intended behaviour, so first pin down the actual behaviour with tests that assert what the code does today — bugs included. Only then change it. These tests are scaffolding: some are deleted once the real behaviour is specified.
What ships with it
2 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.
- 2d ago First seen · 237 lines · 97 tokens per session scan A 64017691b998
tdd-workflow is a skill published in the GitHub repository personamanagmentlayer/pcl (40 stars, last pushed today), licensed Apache-2.0. It adds 97 tokens to every session and 2,006 once invoked, about $0.0005 per session on Opus 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 2026-09-05.
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test-driven-development
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test-driven-development
A test-driven development guide. Test-driven development, or TDD, means writing a test first, confirming that it fails, then writing the smallest code that makes it pass and improving the result.