What belongs in the applicationService package to properly test the onion architecture with ArchUnit?

[darthkali]

I am currently in the process of implementing a simple hexagonal architecture. I have followed the DDD principle and placed the DomainModels alongside the DomainServices in a domain-package. In addition to this, there is the adapter-package, which contains inbound and outbound adapters.

Now, the ports also need to be placed somewhere. Initially, I put them in a third package called application and added this path to the ApplicationService method from ArchUnit. However, this is a problem for ArchUnit because there are now accesses from the domain-package to the application package:

Class <...domain.services...> implements interface <...application.ports.in...> in (...)

Therefore, I have now tried placing the ports in the domain-package, which achieves the desired effect. However, I am now wondering what the application package or the applicationService method is needed for? What should go in there? Or am I misunderstanding something here?

Here is a brief overview of my (final) structure again:

- adapter
  |- inbound
  |- outbound
- domain
  |- model
  |- services
  |- ports
- application
  |- ???
- Application.kt

And here is my current test:

    val `hexagonal architecture is respected`: ArchRule = onionArchitecture()
        .domainModels("$rootPackage.domain.model..")
        .domainServices("$rootPackage.domain.services..", "$rootPackage. domain.ports..")
        .applicationServices("$rootPackage.application.." )
        .adapter("Adapter", "$rootPackage.adapter..")
        .withOptionalLayers(true)