write-tests

write-tests is a skill for Claude Code, Codex from marin-community/marin. It costs 24 tokens per session (363 once invoked), scanned A, original, Apache-2.0.

A guide for adding, changing, or reviewing tests for an explicitly defined behavior or regression. It emphasizes small tests that observe what users or other systems can actually see.

In plain words
What is it for?
Use it to find existing tests, write a regression test before a fix, choose fixtures and mocks, run focused tests, and then run the required broader test and lint checks.
Why use it?
It helps ensure a test would fail when the intended behavior is broken, rather than only checking internal implementation details. It also aligns test choices with the project’s local rules and commands.

Skill for Claude CodeCodex

About the project

Marin is an open-source research program, software platform, and community for developing foundation models such as large language models. Researchers use it for data preparation, tokenization, pretraining, posttraining, evaluation, and related experiments, including work on audio-text, DNA, and protein models. The catalogue entries are add-ons that support workflows around Marin.

marin-community/marin · 3,354 stars · on GitHub

Install

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.

agentmods
npx agentmods add skills/marin-community/marin/write-tests
Any agent
npx skills add marin-community/marin --skill write-tests
Clone the repo
git clone --depth 1 https://github.com/marin-community/marin

Made for: Claude Code, Codex.

Wrote 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.

agentmods badge for write-tests

README.md
[![agentmods](https://agentmods.dev/badge/skills/marin-community/marin/write-tests.svg)](https://agentmods.dev/skills/marin-community/marin/write-tests)
Your own site
<a href="https://agentmods.dev/skills/marin-community/marin/write-tests"><img src="https://agentmods.dev/badge/skills/marin-community/marin/write-tests.svg" alt="Measured on agentmods" height="20"></a>
Per session 24 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 363 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5 $0.00024 $0.00363
Opus 5 $0.00012 $0.00181
Sonnet 5 $0.00005 $0.00073
Haiku 4.5 $0.00002 $0.00036

Measured 5d ago against content hash fbe7a18f976f, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

write-tests 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 5d 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.

.agents/skills/write-tests/SKILL.md · 40 lines

What it actually says

Write Tests

Read these before choosing test style, fixtures, mocks, markers, or commands:

  • root AGENTS.md
  • root TESTING.md
  • the nearest subproject AGENTS.md for files under lib/*
  • package testing docs referenced from that AGENTS.md, such as lib/iris/TESTING.md

Workflow

  1. Find existing tests for the touched behavior before creating a new file.
  2. Check module-specific testing rules for commands, markers, fakes, mocks, and numerical tolerances.
  3. Name the behavior that should fail if the code is wrong.
  4. Write the smallest test that observes that behavior through a public API, structured output, persisted state, or real side effect.
  5. For a bug, write the regression test before the fix and confirm it fails.
  6. Keep test setup realistic but small. Use fixtures and parameterization to remove duplication.
  7. Run the narrow test first, then the relevant package test command. Before a PR, run the repo lint entry point required by AGENTS.md.

Default Commands

  • Run a narrow test path while editing, then run uv run --no-project infra/ci/run_tests.py. Do not override the repository's default marker expression.
  • For package-specific commands, use the relevant lib/*/AGENTS.md or testing doc.

Before a PR, run ./infra/pre-commit.py --changed-files --fix or --all-files as appropriate. Do not substitute uv run pre-commit.

Changes

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.

  1. 5d ago First seen · 40 lines · 24 tokens per session scan A fbe7a18f976f

Subscribe to this mod's changes

write-tests is a skill published in the GitHub repository marin-community/marin (3,354 stars, last pushed today), licensed Apache-2.0. It adds 24 tokens to every session and 363 once invoked, about $0.0001 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 2026-08-30.

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