test-gap-review

test-gap-review is a skill for Claude Code, Codex from yarlson/yarstack. It costs 32 tokens per session (339 once invoked), scanned A, original, MIT.

A review of whether existing tests and other checks truly prove a specific software behavior. It examines normal cases, boundaries, failures, state preservation, cleanup, and outside effects.

In plain words
What is it for?
Use it during validation to find gaps in coverage and define the smallest additional check that would prove an important claim. It also reviews test structure, reproducibility, and risks such as concurrency, restart, and recovery.
Why use it?
It identifies false confidence from weak assertions, incomplete coverage, unsuitable fixtures, or unsupported manual claims. This shows what evidence is still missing without silently changing the tests or code.

Skill for Claude CodeCodex

Part of the yarstack plugin — 38 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/yarlson/yarstack/test-gap-review
Any agent
npx skills add yarlson/yarstack --skill test-gap-review
Clone the repo
git clone --depth 1 https://github.com/yarlson/yarstack

Made for: Claude Code, Codex.

Or install yarstack, the plugin that ships this one along with the rest of its 38 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 test-gap-review

README.md
[![agentmods](https://agentmods.dev/badge/skills/yarlson/yarstack/test-gap-review.svg)](https://agentmods.dev/skills/yarlson/yarstack/test-gap-review)
Your own site
<a href="https://agentmods.dev/skills/yarlson/yarstack/test-gap-review"><img src="https://agentmods.dev/badge/skills/yarlson/yarstack/test-gap-review.svg" alt="Measured on agentmods" height="20"></a>
Per session 32 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 339 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 $0.00032 $0.00339
Opus 5 $0.00016 $0.00169
Sonnet 5 $0.00006 $0.00068
Haiku 4.5 $0.00003 $0.00034

Measured 3d ago against content hash 9aed6af3ce97, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

test-gap-review 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 3d 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.

plugins/yarstack/skills/test-gap-review/SKILL.md · 31 lines

What it actually says

Test Gap Review

Audit verification sufficiency without silently becoming a test-writing or production implementation workflow.

Workflow

  1. Establish the authoritative behavioral contract, comparison scope, and claimed verification.
  2. Map invariants, assumptions, normal behavior, important boundaries, meaningful failures, preserved state, cleanup, and external effects to existing evidence.
  3. Identify weak assertions, fixtures that cannot fail meaningfully, implementation-detail tests, unsupported manual claims, and skipped required commands. Flag example-only evidence when the claim spans a broad input space, operation sequence, concurrent ordering, restart, or recovery, and check that generated failures are reproducible.
  4. Review changed test code as maintained product code. Flag unclear naming or structure, repeated setup that should use a focused helper, helpers that hide scenario data or mix responsibilities, and table-driven cases that do not share one execution path.
  5. Report each material gap with the affected claim, missing evidence, consequence, smallest proving check, and residual risk.
  6. If remediation is authorized, use test-design for test changes and behavior-implement for production behavior; otherwise remain read-only.

For each material claim report:

VERIFIED | NOT VERIFIED | INCONCLUSIVE
Claim: ...
Evidence: ...
Reasoning: ...

Do not chase coverage percentages, demand a stronger method without a concrete risk, add fake-confidence tests, broaden infrastructure, or change production behavior directly.

Finish when material claims have supported statuses and remaining verification risk is explicit.

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. 3d ago First seen · 31 lines · 32 tokens per session scan A 9aed6af3ce97

Subscribe to this mod's changes

test-gap-review is a skill published in the GitHub repository yarlson/yarstack (3 stars, last pushed 6d ago), licensed MIT. It adds 32 tokens to every session and 339 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 2026-08-31.

Related

Other skills, from other repositories

opensrc

Fetch dependency source code to give AI agents deeper implementation context. Use when the agent needs to understand how a library works internally, read source code for a package, fetch implementation details for a dependency, or explore how an npm/PyPI/crates.io package is built. Triggers include "fetch source for"…

vercel-labs/opensrc · 103 tokens

release-cli

Release a new version of the tokenmaxxing CLI to npm. Use when explicitly asked to release or publish @851-labs/tokenmaxxing, including checking main, bumping apps/cli/package.json, updating CHANGELOG.md, committing, tagging cli-vX.Y.Z, pushing, monitoring generated native package publishing, and smoke testing the…

851-labs/tokenmaxxing · 73 tokens

audit-plan-implementation

Independently audit a task attempt or completed run against a frozen plan, checking ownership, evidence, acceptance, and final readiness.

avksp/agent-lifecycle-kit · 31 tokens

agent-first-planning

Create or revise production-ready SDD plans for agent execution, including clarification, specification, freeze inputs, ownership, budgets, and evidence contracts.

avksp/agent-lifecycle-kit · 33 tokens

ship-mobile-app

Build, change, debug, and prepare production mobile apps across domain meaning, local and server state, lifecycle, platform, and release boundaries. Use for non-trivial Flutter, React Native, iOS, or Android work involving persistence, sync, auth, offline behavior, notifications, permissions, native integrations…

aiopshwang/ship-mobile-app · 103 tokens

verify-regression-tests

Verify that a regression test actually detects the defect it claims to guard against. Use after adding or reviewing a bug-fix guard, reproducing the original failure after a fix, or investigating a suspiciously green regression test. Do not use for general TDD, broad test-suite audits, mutation-score optimization…

aiopshwang/verify-regression-tests · 75 tokens