Its goal is to make sure that the original requirements have been met, that the business rules embodied in the system are correct, and to verify that the system works as a coherent whole. This stage of testing is done in close coordination with the eventual users of the system. This is another reason why it's important to have the participation of the end users in gathering requirements. Typically, a limited-scale deployment of the hardware and software is done in order to facilitate the testing. This is probably the most frequently overlooked step.
Documentation serves two purposes.
Technical documentation is used as a guide for future developers to make changes to a system months or even years later. Even the developer who designed and wrote most of a system would be hard-pressed to remember every detail of its implementation after a period of time. User documentation, on the other hand, is the guide to using the system, as well as making the most of its features. User documentation may come in different forms, from printed manuals to online help files. While one of the goals of effective user interface design is to minimize the need for user documentation by making the system easy and intuitive to use, proper documentation is nonetheless important in training both current and new staff in the use of the system.