Device prototyping is an inherent part of any project. A project may require several separate prototypes since not everything can be simulated - all depends on project's complexity and application of innovative solutions.
If a project is less complicated prototyping can be conducted in the circuit itself, thanks to the use of programmable elements.
Another matter is a set of tests conducted during the first run of a device. If necessary, we are able to test each piece separately.
These are just some of the parameters which may require testing. Some devices require initial calibration which may be conducted as a part of the startup process.