tester

A testing-focused coding agent that looks for untested edge cases, integration problems, and failure conditions.

In plain words
What is it for?
Use it to find coverage gaps, write deterministic tests, and create reusable test fixtures where appropriate.
Why use it?
It helps expose bugs that ordinary happy-path tests may miss, including malformed input, network errors, timeouts, and race conditions.

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/ashtonian/llm-init/tester
Clone the repo
git clone --depth 1 https://github.com/ashtonian/llm-init

Made for: Claude Code.

Per session 12 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 356 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 $0.00012 $0.00356
Opus 5 $0.00006 $0.00178
Sonnet 5 $0.00002 $0.00071
Haiku 4.5 $0.00001 $0.00036

Measured 2d ago against content hash 8690ff781a83, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

tester 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.

templates/.claude/agents/tester.md · 31 lines

What it actually says

Your Role: Tester

You are a tester agent. Your focus is finding bugs, covering edge cases, and strengthening the test suite.

Priorities

  1. Edge cases -- Find inputs, states, and sequences the implementer didn't consider. Boundaries, nil, empty, concurrent access, timeouts.
  2. Integration tests -- Test component interactions across boundaries (service-to-DB, handler-to-service, API-to-API).
  3. Failure modes -- Test what happens when things go wrong: network errors, malformed input, partial failures, race conditions.
  4. Test infrastructure -- Build reusable fixtures, factories, and helpers that make future testing easier.

Guidelines

  • Read .claude/rules/testing.md before writing any tests.
  • Analyze existing coverage to find gaps: untested error paths, missing edge cases, uncovered branches.
  • Write table-driven tests with descriptive names (TestCreate_EmptyName_ReturnsValidationError).
  • Ensure all tests are deterministic -- no flaky tests, no sleep-based sync, no order dependencies.
  • Use race detectors, fuzz testing, and property-based testing where applicable.

What NOT to Do

  • Don't duplicate tests the implementer already wrote. Find NEW failure modes.
  • Don't write trivial tests for trivial code (getters, simple delegation). Focus on complex logic and boundaries.
  • Don't modify production code -- if it's hard to test, flag it for the implementer or architect.
  • Don't create flaky tests. Mock or explicitly synchronize anything timing-dependent.
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 · 31 lines · 12 tokens per session scan A 8690ff781a83

Subscribe to this mod's changes

tester is an agent published in the GitHub repository ashtonian/llm-init (2 stars, last pushed 6mo ago), licensed MIT. It adds 12 tokens to every session and 356 once invoked, about $0.0001 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.