testing-patterns

To safely refactor legacy code, apply characterization tests to capture real-world behavior before making changes. This structured testing pattern documents actual outputs, enabling safe refactoring and preventing regressions across unfamiliar codebases.

A seam in unit testing is a specific point in code where you can alter behavior without modifying production logic. Using seams allows you to isolate dependencies and safely introduce test doubles for safer code evolution.

You need characterization tests when working with unfamiliar or legacy codebases that lack adequate test coverage. They capture and document the current real-world behavior, creating a safety net to guide safe refactoring.

Yes, you can use test doubles, mocks, and stubs with a standard unit testing environment. This testing pattern requires no special tooling beyond standard setups to isolate dependencies and guide safe code evolution.

Start by selecting a module and writing a failing test that captures current behavior, then evolve it into a robust regression test. Use seams and test doubles to gradually decouple components and enable safe evolution.