A coding assistant for writing and improving automated tests, including unit tests for individual pieces of code and integration tests for connected parts of a system.

Use it to add test coverage, improve existing tests, name tests clearly, mock external dependencies, and run tests after changes.

It helps you follow the project's existing test framework and conventions instead of designing tests from scratch. It also helps check normal behavior, edge cases, errors, and outside services consistently.

test-writer — Agent for Claude Code by mordilion

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.

Clone the repo

git clone --depth 1 https://github.com/mordilion/ai-instructions-and-prompts

Made for: Claude Code.

Or install ai-iap, the plugin that ships this one along with the rest of its 2 skills, 5 agents.

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.

README.md

[![agentmods](https://agentmods.dev/badge/agents/mordilion/ai-instructions-and-prompts/test-writer/github.svg)](https://agentmods.dev/agents/mordilion/ai-instructions-and-prompts/test-writer)

Your own site

<a href="https://agentmods.dev/agents/mordilion/ai-instructions-and-prompts/test-writer"><img src="https://agentmods.dev/badge/agents/mordilion/ai-instructions-and-prompts/test-writer/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.

Your own site · 80×15

<a href="https://agentmods.dev/agents/mordilion/ai-instructions-and-prompts/test-writer"><img src="https://agentmods.dev/badge/agents/mordilion/ai-instructions-and-prompts/test-writer.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 28 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.

When invoked 175 The whole file, excluding the scripts and references it only reads on demand.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

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.

Model	Per session	Once invoked
Fable 5.1	$0.00028	$0.00175
Opus 5.5	$0.00011	$0.00070
Sonnet 5.5	$0.00006	$0.00035
Haiku 4.5	$0.00003	$0.00017

Measured 2mo ago against content hash 9614063f2c30, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

test-writer 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 2mo 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.

plugin/agents/test-writer.md · 23 lines

What it actually says

You are a test engineer. Write and improve tests following the project's testing rules and conventions.

Before writing tests:

Check the project's test-implementation process in .claude/rules/ if present
Identify the test framework and patterns used in existing tests
Check the project's functions index for relevant patterns

Guidelines:

Use the project's established test framework and patterns
Prefer existing patterns over inventing new ones
Cover happy paths, edge cases, and error scenarios
Keep tests focused and independent
Use descriptive test names that explain the expected behavior
Mock external dependencies appropriately
Run tests after writing to verify they pass

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.

2mo ago First seen · 23 lines · 28 tokens per session scan A 9614063f2c30

Subscribe to this mod's changes

test-writer is an agent published in the GitHub repository mordilion/ai-instructions-and-prompts (1 stars, last pushed 4mo ago), licensed MIT. It adds 28 tokens to every session and 175 once invoked, about $0.0001 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 2026-08-31.

Testing Unit testing

test-writer next to 6 agents from other repositories
Mod	Type	Stars	Last push	Licence	Scan	Tokens	Works with
test-writermordilion/ai-instructions-and-prompts	Agent	1	4mo ago	MIT	A	28	Claude Code
ai-hygiene-auditorathola/claude-night-market	Agent	350	today	MIT	A	48	Claude Code
test-gapswesammustafa/Claude-Code-Everything-You-Need-to-Know	Agent	3.6k	9d ago	none	A	38	Claude Code
pydantic-ai-validatorcoleam00/context-engineering-intro	Agent	14k	8mo ago	MIT	A	46	Claude Code
testerInsajin/autopus-adk	Agent	111	2mo ago	MIT	A	38	Claude Code
verify-apppablomarin/claude-codex-forge	Agent	5	15d ago	MIT	A	15	Claude Code
test-engineerashrafmusa/agenticana	Agent	2	5d ago	MIT	A	49	Claude Code