Domain-Driven Design encourages teams to build systems with clear layers, isolated domain logic, and well-defined boundaries. But over time, these structures erode: infrastructure code leaks into the domain, application services grow too wide, and context boundaries become porous.

This talk introduces a practical and executable approach to preserving DDD architecture using ArchUnit.NET. Architecture tests act like unit tests—but for the codebase structure. They let developers:

- enforce clean layering between Application, Domain, and Infrastructure,
- ensure domain logic is protected from technical concerns,
- and detect unwanted dependencies before they cause harm.

The session is largely live coded: the audience will see how to write architecture tests in C# and integrate them into a continuous build process. All examples use a standalone DDD-style example.

Based on experience from real-world projects, the techniques shown are concrete, pragmatic, and ready to apply in any codebase—starting tomorrow.