Pin Behavior With Early Tests

CHANGE-PIN-BEHAVIOR-WITH-EARLY-TESTS

Summary

Add characterization tests before changing messy behavior when the existing contract is unclear. The baseline separates intentional behavior changes from accidental drift.

Rule

Use early test changes to pin existing behavior when that makes behavior changes easier to review.

Why

Before changing messy behavior, an early test can document what the system currently does. That test gives reviewers a stable baseline, separates characterization from the behavior change, and catches accidental changes during refactoring.

Helps

Makes behavior changes safer and clarifies whether later diffs preserve or intentionally change existing behavior.

Limits

Do not freeze behavior that is obviously wrong unless the test names it as characterization. Skip this when existing tests already pin the relevant contract.

Agent Instruction

Use early tests to pin current behavior before changing messy behavior so reviewers can separate
existing behavior from the intended change.

Mechanisms

Supported by characterization tests, regression fixtures, snapshots, before/after commits, and jj changes that separate test characterization from behavior edits.