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 Cristhianzl/claude-skills-czl --skill writing-testsgit clone --depth 1 https://github.com/Cristhianzl/claude-skills-czlWrote 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/cristhianzl/claude-skills-czl/writing-tests)<a href="https://agentmods.dev/skills/cristhianzl/claude-skills-czl/writing-tests"><img src="https://agentmods.dev/badge/skills/cristhianzl/claude-skills-czl/writing-tests/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/cristhianzl/claude-skills-czl/writing-tests"><img src="https://agentmods.dev/badge/skills/cristhianzl/claude-skills-czl/writing-tests.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector warn
SkillSpector: 1 finding, up to medium
These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →
- medium Excessive Agency · line 28 Skill enables autonomous high-impact decisions without human-in-the-loop verification. Critical operations (destructive commands, financial transactions, data deletion) should require explicit user confirmation.Fix: Add human-in-the-loop confirmation for destructive, irreversible, or high-impact operations. Never auto-execute commands that modify files, send data, or alter system state.
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 | $0.00103 | $0.03255 |
| Opus 5 | $0.00051 | $0.01628 |
| Sonnet 5 | $0.00021 | $0.00651 |
| Haiku 4.5 | $0.00010 | $0.00326 |
Grade A, and why
writing-tests scanned grade A with 1 finding 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 12d 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.
Runs shell commandslowCapability
Expected in a hook, worth knowing in a rule or an instructions file.
Tests are implicitly Linux-only when they hardcode `/tmp`, depend on `\n`-only line endings, call `subprocess.run("ls")`, assume case-sensitive filesystems, or fork worker processes. Fix patterns in `references/multi-pla How it starts
The opening of the file, as written. The whole thing — 224 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Writing Tests
Test code is production code. Same quality bar — naming, structure, immutability, file structure, security. The point of the test suite is to find bugs, not to confirm what the code already does.
Read first (always)
List learnings/ and read every file relevant to the current task. Project-specific test framework choices, fixture conventions, flaky-test hotspots, or coverage carve-outs live there and override the defaults in this SKILL.md. If a learning conflicts with this file, the learning wins — mention it to the user.
Tradeoff — when to apply, when to lighten up
Apply the full discipline (pyramid, AAA, coverage gate, multi-platform matrix) for production code. Lighten the formality for one-off scripts, exploration, or examples under 30 lines — but even then, at least one happy-path test and one adversarial test.
Pre-test analysis (mandatory)
Before writing a single test:
- Identify the test framework. Look for
pytest.ini/jest.config.*/vitest.config.*/*_test.go/build.gradletest deps /*.Tests.csproj/Cargo.toml [dev-dependencies]. Use the framework already in the project. Do NOT introduce a new one. - Identify the mocking library.
unittest.mock/pytest-mock,jest.mock/vitest.mock/sinon/msw,Mockito,gomock/testify/mock,Moq/NSubstitute. Use what's already there. - Identify existing test patterns. How are files named and organized? Are there factories, fixtures, helpers,
conftest.py,__mocks__? Reuse them. Do NOT duplicate. - Identify the linter, formatter, type checker used on test code. Run them in pre-commit (Step 5).
If you introduce a new pattern without checking existing ones, stop and refactor.
Workflow
- Plan coverage from the spec, not the code. List the behaviors the feature exhibits per the requirements. Categorize each as success, error, edge, or boundary. Map each to unit / integration / E2E using the pyramid below. → verify: every behavior from the spec maps to at least one planned test; pure infrastructure glue maps to ≤1.
What ships with it
6 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.
- 12d ago First seen · 224 lines · 103 tokens per session scan A 1ff3f91920d4
writing-tests is a skill published in the GitHub repository Cristhianzl/claude-skills-czl (5 stars, last pushed yesterday), licensed MIT. It adds 103 tokens to every session and 3,255 once invoked, about $0.0005 per session on Opus 5. A static security scan graded it A with 1 finding (runs shell commands). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.
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testing-patterns
Testing strategy: pyramid, AAA, mocks/fakes/stubs, flaky tests, coverage. Triggers: test, fixture, mock, stub, e2e, TDD, Playwright, Cypress, flaky, coverage, property-based.
accessibility-testing
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