legacy-code-safety

Characterization testing lets you document existing behavior before making changes. Write tests that capture how the code currently works, verify they pass, then refactor with confidence using the Red-Green-Refactor loop. This anchors your changes to real behavior and prevents hidden regressions.

Characterization testing writes tests that describe existing behavior in untested code. Use it when you need to modify, delete, or refactor legacy functions without test coverage. It's essential in codebases with low test discipline where tests are your primary safety net.

Identify the legacy function you need to change, write baseline characterization tests that document its current behavior, run tests to confirm they pass, then proceed with small incremental changes. Follow Red-Green-Refactor to validate each step.

Yes. Characterization testing is particularly valuable in dynamically typed languages where tests serve as the primary safety net. The workflow enforces Red-Green-Refactor discipline to catch regressions that static type systems might otherwise catch.

Characterization testing differs from unit testing by documenting existing behavior first rather than ideal behavior. It's a risk-mitigation strategy for untested legacy code, preventing regressions when you lack understanding of how code actually works.