Ever since the inception of Java EE, testing enterprise applications has been a major pain point. Testing business components, in particular, can be very challenging. Often, a vanilla unit test isn't sufficient for validating such a component's behavior. Why is that? The reason is that components in an enterprise application rarely perform operations which are strictly self-contained. Instead, they interact with or provide services for the greater system. They also have declarative functionality which gets applied at runtime. You could say "no business component is an island."

The way the component interacts with the system is just as important as the work it performs. Even with the application separated into more layers than your favorite Mexican dip, to validate the correctness of a component, you have to observe it carrying out its work—in situ. Unit tests and mock testing can only take you so far. Business logic aside, how do you test your component's "enterprise" semantics?

Especially true of business components, you eventually have to ensure that the declarative services, such as dependency injection and transaction control, actually get applied and work as expected. It means interacting with databases or remote systems and ensuring that the component plays well with its collaborators. What happens when your Message Driven Bean can't parse the XML message? Will the right component be injected? You may just need to write a test to explore how the declarative services behave, or that your application is configured correctly to use them. This style of testing needed here is referred to as integration testing, and it's an essential part of the enterprise development process.

Arquillian, a new testing framework developed at JBoss.org, empowers the developer to write integration tests for business objects that are executed inside a container or that interact with the container as a client. The container may be an embedded or remote Servlet container, Java EE application server, Java SE CDI environment or any other container implementation provided. Arquillian strives to make integration testing no more complicated than basic unit testing.

The importance of Arquillian in the Java EE space cannot be emphasized enough. If writing good tests for Java EE projects is some dark art in which knowledge is shared only by the Java gurus, people are either going to be turned off of Java EE or a lot of fragile applications are going to be written. Arquillian is set to become the first comprehensive solution for testing Java EE applications, namely because it leverages the container rather than a contrived runtime environment.

This guide documents Arquillian's architecture, how to get started using it and how to extend it. If you have questions, please use the discussion forum in the top-level Arquillian space on JBoss.org. We also provide a JIRA issue tracking system for bug reports and feature requests. If you are interested in the development of Arquillian, or want to translate this documentation into your language, we welcome you to join us in the Arquillian Development subspace on JBoss.org.