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characterization-testing

Capture current software behavior into characterization tests for safe refactoring.

1|Updated Jan 7, 2026
Search Tags:#refactoring#tests#safety-net#legacy-code#characterization-testing#software-testing
One-click install
npx skills add https://github.com/moogah/claude_skills --skill characterization-testing-moogah
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: characterization-testing
Source: https://github.com/moogah/claude_skills/tree/main/characterization-testing
Command: npx skills add https://github.com/moogah/claude_skills --skill characterization-testing-moogah

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill includes references (resource) components.

What problem does it solve?

Characterization testing captures the current behavior of a system to create a safety net before refactoring, documenting what the code actually does so changes can be made confidently.

Core Features & Use Cases

  • Identify target code paths to test and observe actual behavior.
  • Record observed outputs and state changes in characterization tests to prevent regressions.
  • Evolve characterization tests into proper unit tests over time as understanding grows.
  • Use as a minimal safe refactoring aid to reveal seams and dependencies.

Quick Start

Identify a code path, run it to observe its behavior, and write a characterization test that asserts that observed behavior.

Frequently Asked Questions about characterization-testing

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I safely refactor undocumented legacy code without breaking existing behavior?▼

Characterization testing captures the current behavior of legacy code by recording observed outputs and state changes, creating a regression safety net that enables confident refactoring of undocumented modules.

What is the best way to create a safety net before refactoring change-prone areas?▼

The best way is identifying target code paths, running them to observe actual behavior, and writing characterization tests that assert those observed outputs to prevent regressions during refactoring.

How do I write characterization tests for modules with unknown dependencies?▼

You write characterization tests for legacy modules by observing their actual outputs and state changes, using the tests to reveal seams and dependencies in the legacy code before modifying it.

Can I evolve characterization tests into proper unit tests over time?▼

Yes, you can evolve characterization tests into proper unit tests over time as your understanding of the legacy code grows, enabling a gradual migration from behavior snapshots to structured unit tests.

When do I need characterization testing instead of standard unit testing?▼

You need characterization testing when working with undocumented legacy code or change-prone areas where standard unit tests are absent, allowing you to snapshot existing behavior before refactoring.

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