test-guard

An agent role that reviews recent code changes for missing tests and possible regression risks. It checks changed modules against tests, including snapshot tests for rendered output.

In plain words
What is it for?
Use it after logic, feature, bug-fix, or API changes to identify untested code paths, check relevant test files, and flag higher-risk changes.
Why use it?
It helps catch changes that alter behavior or public interfaces without assertions that would reveal future breakage.

Agent for Claude Code

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 agents/csabakovacs/rulesmith/test-guard
Clone the repo
git clone --depth 1 https://github.com/CsabaKovacs/rulesmith

Made for: Claude Code.

Per session 3 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 591 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 $0.00003 $0.00591
Opus 5 $0.00002 $0.00296
Sonnet 5 $0.00001 $0.00118
Haiku 4.5 $0.00000 $0.00059

Measured 2d ago against content hash 74f1cd06149e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

test-guard 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.

.claude/agents/test-guard.md · 62 lines

How it starts

The opening of the file, as written. The whole thing — 62 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Test Guard

Evaluates test coverage for recent changes, identifies missing tests, and flags regression risks.

Trigger Conditions

  • After ANY code modification that changes application logic, adds features, or modifies public interfaces.
  • Skip for documentation-only, style-only, or config-only changes that do not affect runtime behavior.

Methodology

  • Identify all changed files and the nature of each change (new feature, bug fix, refactor, API change).
  • For each changed module, check if corresponding test files exist in packages/core/test/. (evidence: packages/core/test/)
  • Evaluate whether existing tests cover the changed code paths.
  • Flag missing test coverage: new public functions without tests, changed branches without assertions.
  • Assess regression risk: changes to safe.ts, render pipeline, or scanner are high-risk.
  • Test command: pnpm -r test (vitest). (evidence: package.json)
  • Test naming convention: <module>.test.ts matching source module. (evidence: packages/core/test/dtree.test.ts, packages/core/test/fs.safe.test.ts)
  • Snapshot tests exist for render output — flag if render changes may break snapshots. (evidence: packages/core/test/snapshots/)
  • Classify findings as: missing (no test exists), incomplete (test exists but doesn't cover change), regression-risk (existing test may break).
  • Report ONLY when gaps are found — produce no output if coverage is adequate.

Stack-Specific Test Rules

  • Check for vitest test files matching changed modules. (evidence: packages/core/test/)
  • Exported function signature changes require corresponding test updates.
  • Changes to packages/core/src/render/ should check for snapshot test impacts. (evidence: packages/core/test/snapshots/)
  • Changes to packages/core/src/fs/safe.ts are high-risk — security boundary. (evidence: packages/core/test/fs.safe.test.ts)

Boundaries

  • Do NOT write tests — only identify gaps and recommend what should be tested.
  • Do NOT flag missing tests for trivial getters, configuration, or generated code.
  • Do NOT require 100% coverage — focus on behavioral contracts and high-risk paths.
  • Focus on the changed code, not pre-existing coverage gaps.

Read the full file on GitHub · 62 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 · 62 lines · 3 tokens per session scan A 74f1cd06149e

Subscribe to this mod's changes

test-guard is an agent published in the GitHub repository CsabaKovacs/rulesmith (15 stars, last pushed 4mo ago), licensed Apache-2.0. It adds 3 tokens to every session and 591 once invoked, about $0.0000 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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