write-unit-test

write-unit-test is a skill for Claude Code, Codex from patrick-fu/awesome-skills. It costs 33 tokens per session (445 once invoked), scanned A, original, MIT.

A guide for writing unit tests, which check one piece of application code in isolation, for production business logic.

In plain words
What is it for?
Use it to create, review, or improve tests for normal, asynchronous, error, integration-boundary, and mock-heavy code.
Why use it?
It helps tests verify real user-visible behavior and catch regressions without depending on fragile implementation details.

Skill for Claude CodeCodex

Part of the engineering-workflow plugin — 3 skills shipped together

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/patrick-fu/awesome-skills/write-unit-test
Any agent
npx skills add patrick-fu/awesome-skills --skill write-unit-test
Clone the repo
git clone --depth 1 https://github.com/patrick-fu/awesome-skills

Made for: Claude Code, Codex.

Or install engineering-workflow, the plugin that ships this one along with the rest of its 3 skills.

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-unit-test

README.md
[![agentmods](https://agentmods.dev/badge/skills/patrick-fu/awesome-skills/write-unit-test.svg)](https://agentmods.dev/skills/patrick-fu/awesome-skills/write-unit-test)
Your own site
<a href="https://agentmods.dev/skills/patrick-fu/awesome-skills/write-unit-test"><img src="https://agentmods.dev/badge/skills/patrick-fu/awesome-skills/write-unit-test.svg" alt="Measured on agentmods" height="20"></a>
Per session 33 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 445 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 $0.00033 $0.00445
Opus 5 $0.00016 $0.00222
Sonnet 5 $0.00007 $0.00089
Haiku 4.5 $0.00003 $0.00044

Measured 5d ago against content hash 234ff0fee0c3, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

write-unit-test 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.

write-unit-test/SKILL.md · 48 lines

What it actually says

Write Unit Tests

Use this advisory skill for production product or business code. Prompt, skill, and agent-behavior evaluation need different methods.

Method

  1. Read the exported surface, its callers, nearby tests, and shared test utilities. State one caller-visible contract and the regression risk it guards.
  2. Write one test whose name states the expected outcome. Keep the decisive input visible at the call site; split distinct behaviors.
  3. Assert observable effects: returned values, public state, stable error types or codes, persistence, emitted events, rendered UI, or a boundary call when that call is itself the contract.
  4. Build the smallest realistic setup. Match real data and error shapes; isolate only the lowest true external boundary.
  5. For a regression or test-first change, confirm the test is red for the intended reason before relying on it.
  6. Run the focused test and relevant suite. Finish only when breaking the stated contract would fail the test while harmless internal refactoring would not.

Judgment

  • Prefer exact domain outcomes and meaningful fields. Use full snapshots or full error messages only when the entire representation is the contract.
  • Use a real dependency or small fake when its behavior matters. Mocks fit slow, flaky, costly, or external boundaries; verify collaborator calls only when the call is externally meaningful.
  • Wait for the condition or event that proves async completion. Use a controlled clock or fixed delay only when timing itself is the contract.
  • Keep contract-relevant fields in test doubles; partial mock shapes can hide downstream assumptions.
  • Let builders remove noise while exposing the value that makes the case meaningful.
  • Treat private-state access as a coupling signal. Keep test-only affordances in test utilities and production APIs product-driven.
  • Match the repository's existing framework, naming, placement, and helper conventions.
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 · 48 lines · 33 tokens per session scan A 234ff0fee0c3

Subscribe to this mod's changes

write-unit-test is a skill published in the GitHub repository patrick-fu/awesome-skills (57 stars, last pushed 2d ago), licensed MIT. It adds 33 tokens to every session and 445 once invoked, about $0.0002 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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