In theory your right, you put whatever you want in the WAR it deploys.
The entire point of Arquillian is to test in a live container, which means using it for things that will interact with the container services. They love to put up examples of stuffing 3 classes into a war and testing it, to which I say, why? It makes sense if your testing a CDI extension (who incidentally seem to be the only people using Arquillian). If I wanted to test 3 classes from my app I'd mock the injects with mockito. Its far faster and easier to use mockito to inject instances, especially since mockito can instrument those injections allowing you to assert method call information.
Where this all falls apart is where Arquillian should shine: integration tests. e.g. put up a functional JSF controller/view and fire requests at it with JSFUnit. You now have to package up enough stuff into your war to get a functional JSF environment running. Arquillian doesn't help you at all to figure out what dependencies you need to include to just get JSF running. As a result you end up playing games trying to get the WAR to include what it needs to run which can be much harder than it sounds due to the way much of the EE6 stack is layered and intertwined. You end up having to include a ludicrous amount of stuff to get JSF running. Or you just say 'fuck it' and tell Arquillian to include your entire pom and get a huge deploy. On top of this is managing your own dependencies. Is your view modularized and using 5 different sub views and supporting controllers (and associated helpers?). Its all up to you to track and manage this. Its like being thrown back into a world without maven for every single test case you try to setup. I found I spent more time trying to figure out what I needed to deploy than I did writing tests.
Also your completely screwed if you try to do a service layer down to database integration test and your using hibernate. Waiting for hibernate to start up on every test class is brutal. Getting rid of hibernate makes testing and many other things so much easier. If you stop to think about how much crap exists in the stack just to deal with hibernates session lifecycle and transaction requirements its amazing. In my current app I have about ~65 entity and ~70 tables, switching from Hibernate to Ebean and ditching the libraries I no longer needed to deal with hibernates session management dropped my final war size by ~15MB (40%), cut startup time in half, and allowed me to remove over a thousand lines of code.
The entire point of Arquillian is to test in a live container, which means using it for things that will interact with the container services. They love to put up examples of stuffing 3 classes into a war and testing it, to which I say, why? It makes sense if your testing a CDI extension (who incidentally seem to be the only people using Arquillian). If I wanted to test 3 classes from my app I'd mock the injects with mockito. Its far faster and easier to use mockito to inject instances, especially since mockito can instrument those injections allowing you to assert method call information.
Where this all falls apart is where Arquillian should shine: integration tests. e.g. put up a functional JSF controller/view and fire requests at it with JSFUnit. You now have to package up enough stuff into your war to get a functional JSF environment running. Arquillian doesn't help you at all to figure out what dependencies you need to include to just get JSF running. As a result you end up playing games trying to get the WAR to include what it needs to run which can be much harder than it sounds due to the way much of the EE6 stack is layered and intertwined. You end up having to include a ludicrous amount of stuff to get JSF running. Or you just say 'fuck it' and tell Arquillian to include your entire pom and get a huge deploy. On top of this is managing your own dependencies. Is your view modularized and using 5 different sub views and supporting controllers (and associated helpers?). Its all up to you to track and manage this. Its like being thrown back into a world without maven for every single test case you try to setup. I found I spent more time trying to figure out what I needed to deploy than I did writing tests.
Also your completely screwed if you try to do a service layer down to database integration test and your using hibernate. Waiting for hibernate to start up on every test class is brutal. Getting rid of hibernate makes testing and many other things so much easier. If you stop to think about how much crap exists in the stack just to deal with hibernates session lifecycle and transaction requirements its amazing. In my current app I have about ~65 entity and ~70 tables, switching from Hibernate to Ebean and ditching the libraries I no longer needed to deal with hibernates session management dropped my final war size by ~15MB (40%), cut startup time in half, and allowed me to remove over a thousand lines of code.