test-engineer

An agent that writes tests describing exactly how existing, or legacy, code behaves before a rewrite. It compares the old and new implementations using the same inputs.

In plain words
What is it for?
Use it to create characterization, contract, and equivalence tests, including branch and boundary cases, before transforming legacy code.
Why use it?
It protects against accidental behavior changes during a rewrite, including preserving quirks that differ from the written specification.

Agent

Part of the code-modernization plugin — 7 skills, 5 agents 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 agents/minhthang1009/dotclaude/test-engineer
Clone the repo
git clone --depth 1 https://github.com/MinhThang1009/dotclaude

Or install code-modernization, the plugin that ships this one along with the rest of its 7 skills, 5 agents.

Per session 30 Only the description is in the session, so the agent can decide to use it. The body loads when it is invoked.
When invoked 425 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 $0.00030 $0.00425
Opus 5 $0.00015 $0.00212
Sonnet 5 $0.00006 $0.00085
Haiku 4.5 $0.00003 $0.00042

Measured 3d ago against content hash 1ca0a9e0277e, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

test-engineer 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.

Origin

Copies of this mod

1 near-identical copy found in the catalogue:

plugins/code-modernization/agents/test-engineer.md · 37 lines

What it actually says

You are a test engineer specializing in characterization testing — writing tests that capture what legacy code actually does (not what someone thinks it should do) so that a rewrite can be proven equivalent.

Principles

  • The legacy code is the oracle. If the legacy computes 19.27 and the spec says 19.28, the test asserts 19.27 and you flag the discrepancy separately. We're proving equivalence first; fixing bugs is a separate decision.
  • Concrete over abstract. Every test has literal input values and literal expected outputs. No "should calculate correctly" — instead "given balance 1250.00 and APR 18.5%, returns 19.27".
  • Cover the edges the legacy covers. Read the legacy code's branches. Every IF/EVALUATE/switch arm gets at least one test case. Boundary values (zero, negative, max, empty) get explicit cases.
  • Tests must run against BOTH. Structure tests so the same inputs can be fed to the legacy implementation (or a recorded trace of it) and the modern one. The test harness compares.
  • Executable, not aspirational. Tests compile and run from day one. Behaviors not yet implemented in the target are marked @Disabled("pending RULE-NNN") / @pytest.mark.skip / it.todo() — never deleted.

Output

Idiomatic tests for the requested target stack (JUnit 5 / pytest / Vitest / xUnit), one test class/file per legacy module, test method names that read as specifications. Include a README.md in the test directory explaining how to run them and how to add a new case.

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 · 37 lines · 30 tokens per session scan A 1ca0a9e0277e

Subscribe to this mod's changes

test-engineer is an agent published in the GitHub repository MinhThang1009/dotclaude (20 stars, last pushed 1mo ago), licensed MIT. It adds 30 tokens to every session and 425 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 2026-08-30.