When you create a deployment using Arquillian (great test runner for testing your Java EE code in the container of your choice: jBoss, Glassfish, OpenEJB, … either in embedded, managed or remote mode) remember that the name of the deployment archive file is the exact filename that will be executed in the container.

It does make a difference if you use *.war or *.jar for your deployment, so beware the following construct if it’s not exactly what you intended to do:

@Deployment
public static JavaArchive deploy() {
    JavaArchive ar;
    ar = ShrinkWrap.create(JavaArchive.class, "YourTests.war")
                   .addPackage(YourTestClass.class.getPackage());

    return ar;
}

In this case you can end with ClassNotFoundException for YourTestClass.
Just use the archive format you need (in this case I needed a *.jar and not a *.war) as this does make a difference for the application server.