We are talking about a Java EE application—but it could be generalized to any application if we talk about packaging—so we deploy the application into a server. Even embedded applications are packaging (bundling) a server in their deliverable. As with all the previous points, it is important to align it with the target system: the production environment.
Concretely, it means that you shouldn't test against a WildFly server if your production environment is using Apache TomEE or GlassFish.
A server is not far from your application if we talk about the way it is developed and packaged. This means that it embeds several libraries selected by the server vendor. The direct implication is that a server version embeds several library ...
