In many legacy systems, the code does not reflect the intended architecture, either because it gradually drifted away over time or because a clear target architecture only emerged after months or years of development. This slows down feature development, increases defect rates, adds cognitive load, and makes onboarding new team members more difficult.

This talk demonstrates, through live coding with Java and ArchUnit, how to define architectural rules as executable tests and integrate them step by step into an existing codebase. With this approach, the team can move the system incrementally toward the target architecture while the tests ensure that no new architectural violations are introduced.

After this session, participants will be able to define architectural rules and integrate them as tests into their own legacy codebases.