Refactoring

Refactoring Skill

Restructures existing code without changing behavior, in small atomic steps each backed by a green test suite. Does NOT add features in the same change — refactoring and feature work travel in separate PRs.

When to Use

• A function, class, or file has grown unmanageable.
• Duplication is spreading across modules.
• The demand-elegance skill flagged a hacky solution.
• Names no longer reflect purpose after a domain shift.
• Before adding a new feature into a messy area.
• NOT when there is no test coverage and the change is high-risk — write tests first.

Prerequisites

• Working test suite (or willingness to write characterization tests first).
• git for atomic commits per transformation.
• The view, edit, grep, and glob Copilot tools.
• A baseline run of the test suite passing (proven, not assumed).

How to Run

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1. Run the full test suite. Confirm green baseline.
2. If no tests cover the target, write characterization tests; commit separately.
3. Apply one named transformation.
4. Re-run tests. If red, revert.
5. Commit. Repeat for next transformation.
6. Final pass: full suite + review of the whole diff.

Quick Reference

Procedure

Step 1: Establish the Safety Net

Identify tests covering the target with grep / glob. Run them via the powershell tool. If they fail or do not exist, write characterization tests first and commit them in a separate commit before any refactor.

Step 2: Name the Transformation

Each step in the refactor must have a name from the rubric above ("extract method", "introduce parameter object", "rename for clarity"). If you cannot name it, you are freelancing — stop.

Step 3: One Transformation, One Commit

For each step:

1. Apply the change with the edit tool.
2. Run the full test suite.
3. If red, revert immediately.
4. If green, commit with message refactor: <named transformation>.

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refactor: extract validateInput() from handleRequest()
refactor: rename UserManager to UserRepository
refactor: move email logic to NotificationService
refactor: delete unused formatLegacyDate()

Step 4: Verify the Whole

Run the full suite a final time. Review the cumulative diff (git diff main). Ask: is the result actually clearer, or just rearranged? If not clearer, revert.

Pitfalls

• DO NOT refactor without a green test baseline. You are gambling, not refactoring.
• DO NOT mix refactor and feature work in one PR. Reviewers cannot tell signal from noise.
• DO NOT rename a symbol without searching every reference first (grep on the symbol).
• DO NOT rewrite for a hypothetical future ("we might need this pluggable"). Refactor for today.
• DO NOT big-bang refactor across the whole repo in one commit — small atomic steps, always.

Verification

• Test suite is green before the first transformation.
• Test suite is green after every commit.
• Each commit is named refactor: <transformation>.
• No public API changed (or, if it did, callers were updated in the same PR).
• Final diff is meaningfully clearer than the starting code.