Assembling, testing, and operating a process control system in a controlled environment prior to plant implementation according to a test plan to ensure that it performs properly and meets all requirements of the functional specification. Staging is performed after the standard vendor system acceptance test has been conducted and is done under the end user's supervision to thoroughly exercise all essential control system function. Testing often includes some type of simulation of the actual plan operation with real or simulated inputs to test key application-related functions, such as program interaction.