I think it would be easier for all of us to understand if you elaborated on what you think the issues are. What concrete things are you missing from ExUnit and documentation, what do you wish was different?
Not only this article dumps significant cognitive load on the reader. It's not well digested and not a soft landing into the subject. Worst of all, many Elixir articles assume familiarity with GenStage.
Compare it to this, which is not the best example but is a much more soft landing. https://doc.akka.io/libraries/akka-core/current/typed/actors...