nw-mutation-test

nw-mutation-test is a skill for Claude Code from nWave-ai/nWave. It costs 33 tokens per session (1,332 once invoked), scanned A, original, MIT.

A testing technique that deliberately makes small changes, or mutations, to implementation code and checks whether the test suite detects them. The results show how well tests would catch realistic bugs.

In plain words
What is it for?
Use it after implementing a feature to measure test quality for the changed files and identify weak test cases.
Why use it?
A passing test suite can still miss important failures. Mutation testing exposes tests that pass without checking the behavior they are meant to protect.

Skill for Claude Code

Written for Claude Code: user-invocable in frontmatter. Also seen: mentions CLAUDE.md.

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/nwave-ai/nwave/nw-mutation-test
Any agent
npx skills add nWave-ai/nWave --skill nw-mutation-test
Clone the repo
git clone --depth 1 https://github.com/nWave-ai/nWave

Made for: Claude Code.

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 nw-mutation-test

README.md
[![agentmods](https://agentmods.dev/badge/skills/nwave-ai/nwave/nw-mutation-test.svg)](https://agentmods.dev/skills/nwave-ai/nwave/nw-mutation-test)
Your own site
<a href="https://agentmods.dev/skills/nwave-ai/nwave/nw-mutation-test"><img src="https://agentmods.dev/badge/skills/nwave-ai/nwave/nw-mutation-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 1,332 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 5.1 $0.00033 $0.01332
Opus 5 $0.00016 $0.00666
Sonnet 5 $0.00007 $0.00266
Haiku 4.5 $0.00003 $0.00133

Measured 2d ago against content hash effe610a3005, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-05, from the pricing page.

Security

Grade A, and why

nw-mutation-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 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.

nWave/skills/nw-mutation-test/SKILL.md · 128 lines

How it starts

The opening of the file, as written. The whole thing — 128 lines — stays where its author put it; the contents beside it link to each section on GitHub.

NW-MUTATION-TEST: Feature-Scoped Mutation Testing

Wave: QUALITY_GATE Agent: Crafter (nw-software-crafter)

Overview

Run mutation testing against implementation files from the current feature. Extracts targets from the execution-log.json (see Target extraction)|generates feature-scoped configs|delegates to software-crafter. Uses cosmic-ray (Python)|PIT (Java)|Stryker (JS/TS/C#).

Mutation Testing Strategy

Projects declare a strategy via ## Mutation Testing Strategy in CLAUDE.md: per-feature | nightly-delta | pre-release | disabled.

Default (when unspecified): nightly-delta — the recommended mode. CI runs mutmut nightly against modules changed since the last run (the delta), keeping per-feature delivery gates fast. /nw-mutation-test performs an explicit, on-demand feature-scoped run regardless of strategy; under nightly-delta the in-wave Phase 5 gate is skipped and the work is handled by the CI nightly pipeline.

Target extraction

Implementation files are selected from the execution-log.json (completed_steps[].files_modified.implementation).

Context Files Required

  • docs/feature/{feature-id}/deliver/execution-log.json - Implementation file extraction
  • scripts/mutation/generate_scoped_configs.py - Automated config generation (if available)

Pre-Invocation

Orchestrator performs before delegating:

  1. Extract files — Read execution-log.json and extract implementation files from completed_steps[].files_modified.implementation. Gate: file list non-empty.
  2. Verify on disk — Check all extracted files exist on disk. Gate: zero missing files.
  3. Detect language — Scan config files (pyproject.toml, pom.xml, package.json, etc.) to select tool. Gate: language identified.
  4. Confirm tests pass — Run pytest -x {test_scope} (or equivalent). Gate: exit code 0, no failures.
  5. Ensure mutation venv — For Python, verify .venv-mutation/ exists with cosmic-ray installed. Gate: cosmic-ray --version succeeds.

Read the full file on GitHub · 128 lines

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. 2d ago First seen · 128 lines · 33 tokens per session scan A effe610a3005

Subscribe to this mod's changes

nw-mutation-test is a skill published in the GitHub repository nWave-ai/nWave (605 stars, last pushed 6d ago), licensed MIT. It adds 33 tokens to every session and 1,332 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 2026-09-03.