tdd-legacy

tdd-legacy is a skill for Claude Code from msbaek/msbaek-claude-plugins. It costs 67 tokens per session (1,695 once invoked), scanned A, original, no licence file.

A workflow for adding tests to existing code that has no tests. It first records the current behavior with characterization tests, gets approval for that behavior, and checks the tests with mutation testing before handing the code to further improvements.

In plain words
What is it for?
Use it when adding tests to old code, building a behavior-preserving safety net, or preparing legacy code for refactoring.
Why use it?
It creates a safety net before changing legacy code, including behavior that may be undocumented.

Skill for Claude Code

Written for Claude Code: argument-hint in frontmatter.

Part of the msbaek-tdd plugin — 28 skills, 10 agents, 2 hooks shipped together

Good fit Use it when adding tests to old code, building a behavior-preserving safety net, or preparing legacy code for refactoring.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/msbaek/msbaek-claude-plugins/tdd-legacy
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.

Any agent
npx skills add msbaek/msbaek-claude-plugins --skill tdd-legacy
Clone the repo
git clone --depth 1 https://github.com/msbaek/msbaek-claude-plugins

Made for: Claude Code.

Or install msbaek-tdd, the plugin that ships this one along with the rest of its 28 skills, 10 agents, 2 hooks.

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 tdd-legacy

README.md
[![agentmods](https://agentmods.dev/badge/skills/msbaek/msbaek-claude-plugins/tdd-legacy/github.svg)](https://agentmods.dev/skills/msbaek/msbaek-claude-plugins/tdd-legacy)
Your own site
<a href="https://agentmods.dev/skills/msbaek/msbaek-claude-plugins/tdd-legacy"><img src="https://agentmods.dev/badge/skills/msbaek/msbaek-claude-plugins/tdd-legacy/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for tdd-legacy

Your own site · 80×15
<a href="https://agentmods.dev/skills/msbaek/msbaek-claude-plugins/tdd-legacy"><img src="https://agentmods.dev/badge/skills/msbaek/msbaek-claude-plugins/tdd-legacy.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 67 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,695 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin unknown 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 5.1 $0.00067 $0.01695
Opus 5 $0.00034 $0.00847
Sonnet 5 $0.00013 $0.00339
Haiku 4.5 $0.00007 $0.00169

Measured yesterday against content hash 656208034e00, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-09, from the pricing page.

Security

Grade A, and why

tdd-legacy 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 yesterday.

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.

msbaek-tdd/skills/tdd-legacy/SKILL.md · 115 lines

The source is not reproduced here

No licence file

A repository with no LICENSE is all rights reserved by default, so the body is not copied here. The metadata, the measurements and the link are.

Read it on GitHub

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. yesterday Changed 656208034e00
  2. 6d ago Changed · +1 lines d1304423e794
  3. 9d ago First seen · 114 lines · 67 tokens per session scan A 26073d677976

Subscribe to this mod's changes

tdd-legacy is a skill published in the GitHub repository msbaek/msbaek-claude-plugins (8 stars, last pushed 2d ago), with no licence file. It adds 67 tokens to every session and 1,695 once invoked, about $0.0003 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.