Testing

Tests document intended code behavior and prove that behavior still holds after changes. Testing enables sustainable software delivery speed by preserving confidence that the system still works. After responsibility extraction, each focused class can be tested independently. UserService tests do not require email or logging setup after those concerns are removed from the class. NotificationService tests do not require database setup after database concerns are separated. Easier tests validate that the refactor genuinely separated concerns. Testing is a form of risk management rather than only a technical preference. Testing a God Object is painful because it requires setting up too many surrounding dependencies. A useful testing system lets engineers verify expected behavior after code changes.