<tool_restrictions> Ask one question at a time. In Claude Code use AskUserQuestion; elsewhere ask a single concise plain-text question. Keep any lead-in to 2-3 sentences. Don't narrate missing tools or fallbacks.

EnterPlanMode and ExitPlanMode are banned. This skill is Arc's own structured testing process. </tool_restrictions>

<arc_runtime> Requires the full Arc bundle. Arc-owned paths (agents/, references/, disciplines/, templates/, scripts/, rules/, skills/) resolve from the plugin root — the directory containing agents/ and skills/. Everything else is the user's repository. </arc_runtime>

Characterization Testing Workflow

Backfill focused tests around existing code before a risky change. The goal is not "more tests" in the abstract; it is a trustworthy safety net around behavior that must survive a refactor, migration, or bug fix.

Use this skill when: