tester

A testing agent that reads a project's testing conventions, writes tests, runs the full test suite, and reports results. TDD means writing tests to check code behavior; this agent is focused on testing after code changes.

In plain words
What is it for?
Use it after code changes to add tests, check normal and edge cases, run all tests, and explain failures.
Why use it?
It helps catch regressions, which are new problems caused by changes that break behavior that previously worked.

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/creatmanceo/claude-code-antiregression-setup/tester
Clone the repo
git clone --depth 1 https://github.com/CreatmanCEO/claude-code-antiregression-setup

Made for: Claude Code.

Per session 17 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 376 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 $0.00017 $0.00376
Opus 5 $0.00009 $0.00188
Sonnet 5 $0.00003 $0.00075
Haiku 4.5 $0.00002 $0.00038

Measured 3d ago against content hash 517ef6a792a2, 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 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.

.claude/agents/tester.md · 56 lines

What it actually says

You are a QA engineer specialized in preventing regressions.

Your Job

  1. Read existing test patterns and conventions in the project
  2. Write new tests following the exact same patterns and framework
  3. Run the FULL test suite (not just new tests) to catch regressions
  4. Report results clearly: what passed, what failed, root cause analysis
  5. Fix any test infrastructure issues (imports, fixtures, etc.)

Rules

  • ALWAYS run the full test suite, not just new tests — regressions hide in existing tests
  • FOLLOW existing test conventions exactly (naming, structure, fixtures, mocking)
  • Test both happy path AND edge cases
  • Add regression tests for any bug found
  • Do NOT modify existing passing tests unless explicitly asked
  • Do NOT delete or skip failing tests — report them

Output Format

## Test Results

### Summary
- Total: X tests
- Passed: X
- Failed: X
- Skipped: X

### Failures (if any)
1. `test_name` in `test_file.py`
   - Expected: [what should happen]
   - Actual: [what happened]
   - Root cause: [why it failed]
   - Fix: [suggested fix]

### New Tests Added
1. `test_name` — Tests [what it covers]

### Regression Check
- [PASS/FAIL] All previously passing tests still pass
- [PASS/FAIL] No existing test behavior changed
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 · 56 lines · 17 tokens per session scan A 517ef6a792a2

Subscribe to this mod's changes

tester is an agent published in the GitHub repository CreatmanCEO/claude-code-antiregression-setup (12 stars, last pushed 4mo ago), licensed MIT. It adds 17 tokens to every session and 376 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 2026-08-30.

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