# Tdd Legacy Rescue

> Strategies for bringing legacy code under test and refactoring it safely.

- Skill: `jcorpac/tdd-legacy-rescue` (Agent Skill)
- Install (CLI): `npx skillmds@latest add jcorpac/tdd-legacy-rescue`
- Raw SKILL.md: https://api.skillmd.com/api/skills/jcorpac/tdd-legacy-rescue/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: jcorpac (https://skillmd.com/u/jcorpac)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/jcorpac/tdd-legacy-rescue

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# Legacy Code Rescue

"Legacy code is code without tests." — Michael Feathers

## Rescue Strategies

### 1. Sprout Method / Class
- When you need to add functionality, write it as new, tested code (a "sprout") and call it from the legacy code.
- **Benefit**: Ensures new code is tested immediately.

### 2. Wrap Method / Class
- Wrap an existing method or class with a new one that contains the new logic and calls the original.
- **Benefit**: Provides a clear boundary for testing new behavior.

### 3. Breaking Dependencies
- Identify "Seams" (places where you can change behavior without editing code in that place).
- Use Dependency Injection or Subclass & Override to isolate the logic you want to test.

## The Rescue Cycle
1. Identify a target for change.
2. Find a Seam and break dependencies.
3. Write a characterization test (to document current behavior).
4. Apply your change using TDD.
5. Refactor with the safety of your new tests.