refactoring_strategies

Start by writing characterization tests that document what the code currently does, not what it should do. Then make one small change at a time, run the test suite after each change, and commit atomically so any regression can be isolated and reverted.

The Strangler Fig pattern gradually replaces an old system by wrapping it with new functionality instead of rewriting it all at once. New features are built around the legacy code until the old implementation can be safely removed.

Avoid refactoring when a deadline is very close, test coverage is low, or you do not yet understand the system. Refactoring without a safety net of tests risks introducing regressions that are hard to detect and diagnose.

Write characterization tests first to capture current behavior, and use golden master snapshot tests for large outputs. Do not modify the code until the area being refactored reaches full test coverage.

A kill switch uses a feature flag to revert to the old code within seconds if the refactored version causes problems. Combined with monitoring error rates and latency, it lets you run old and new implementations in parallel safely.