Distribute test sources in modularized project

I use this architecture in my android app inspired by Jeroen Mols:

Each module contains its own unit tests independent if it's a feature or library module.

Currently, I have to duplicate code like my testing rules as I didn't find a way to propagate test code from my core module into the module's tests.

This is possible for production code of cource but also for testing? What's the correct way to do this?