User acceptance testing should already be well understood. Essentially, the system should be tested by the users who will be using it after it has been deployed to a production environment. For many systems, the BizTalk solution will be invisible to the users; that is, they might be interacting with applications that in turn interact with BizTalk. Regardless of the scenario, the system needs to be tested in the context of the bigger picture. Typically, user acceptance testing should be designed to ensure that the system meets functional requirements. For some scenarios, the nonfunctional requirements might also need to be validated by the users, depending on the scenarios for which the solution has been designed.