If the tests are properly scripted, they can be integrated into a real-time monitoring system. In fact, if your monitoring system is already doing all the right tests, you shouldn’t need anything else during your upgrade. (See Chapter 22 for more discussion about service monitoring.)
It is rare that all tests can be automated and added to the monitoring system. For example, load testing—determining how the system performs under simulated amounts of work—often cannot be done on a live system. However, being able to run these tests during otherwise low-usage hours or on demand when debugging a problem can make it easy to track down problems.