In system testing, the whole data warehouse application is tested together. The components are tested to ensure that they work properly together, that they do not cause system resource bottlenecks, and so on. Again, because of the size of a data warehouse system, it is usually possible to perform only minimal system testing before the test plan proper can be enacted. So any pre-plan system testing is normally carried out on a radically cut down version of the system environment. Such tests are useful only in highlighting inconsistencies in the data warehouse components, and will give no real indication of performance or resource issues.