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 krzysztofsurdy/code-virtuoso --skill tddgit clone --depth 1 https://github.com/krzysztofsurdy/code-virtuosoWrote 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/krzysztofsurdy/code-virtuoso/tdd)<a href="https://agentmods.dev/skills/krzysztofsurdy/code-virtuoso/tdd"><img src="https://agentmods.dev/badge/skills/krzysztofsurdy/code-virtuoso/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/krzysztofsurdy/code-virtuoso/tdd"><img src="https://agentmods.dev/badge/skills/krzysztofsurdy/code-virtuoso/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 | $0.00069 | $0.02587 |
| Opus 5.5 | $0.00028 | $0.01035 |
| Sonnet 5.5 | $0.00014 | $0.00517 |
| Haiku 4.5 | $0.00007 | $0.00259 |
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 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 — 166 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Test-driven development loop
Write one failing test, make it pass with the least code, clean up while the tests stay green, repeat. The loop is useful for agents for a specific reason: a test that has never failed proves nothing. If you only ever see tests pass, you cannot tell a test that checks the behavior from one that checks nothing. Watching the failure is what makes the later pass meaningful.
Each step produces evidence: command output you can quote. Without it the loop has not been run, only described.
For test strategy, the pyramid, and test-double theory (mocks, stubs, fakes, London versus Chicago school), see the testing skill. This playbook covers the procedure, not those concepts.
Core principles
| Principle | Meaning |
|---|---|
| No production code without a failing test first | The test defines the behavior; the code only satisfies it |
| One test at a time | Small steps keep the cause of any failure obvious |
| Show the red | Run the test and read the failure. It must fail for the reason you expect |
| Minimum code to green | Write only what the current test needs. More code is untested code |
| Refactor only on green | Cleanup while red hides whether you broke something |
| Test behavior, not implementation | A test should survive a refactor that keeps behavior the same |
Step 0: Prepare
- Find the project's test command and how to run a single test (check
AGENTS.md,CLAUDE.md, theMakefile,package.json,composer.json, CI config). Do not guess. - Run the existing suite once. Record the result. A suite that is already red must be understood before you add to it.
- Pick the smallest behavior to start with. If a spec exists with requirement IDs and WHEN/THEN criteria (see
spec-driven-development), each criterion is one or more tests. - Find the right seam (see below) and an existing test file in the same area to copy conventions from.
The loop
1. Red: write one failing test
Write a single test for one behavior. Name it after the behavior (rejects_expired_token), not the method. Use arrange, act, assert, with one reason to fail.
What ships with it
1 file 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 · 166 lines · 69 tokens per session scan A 10961e04cdac
tdd is a skill published in the GitHub repository krzysztofsurdy/code-virtuoso (36 stars, last pushed yesterday), licensed MIT. It adds 69 tokens to every session and 2,587 once invoked, about $0.0003 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 2026-10-22.
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test-driven-development
Use when implementing any feature or bugfix, before writing implementation code.
test-driven-development
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