Normally you build 2 prototypes of a spacecraft; one is called the engineering prototype (or model), and the other one is called the protoflight.
Both must be identical, but the engineering model is normally reassembled several times during development and testing, and will stay on earth as a faithful reference of the flight model.
The protoflight must be handled with extreme care (to avoid any damaging of connectors, or ageing of mechanical components). It is the protoflight that must undergo all final qualification tests (thermal-vacuum, vibration, acoustic, outgassing).
Note that for beasts such as telecommunications satellites, there is no budget for building a complete engineering model. These are integrated based on already tested and reliable components (avionics, propulsion, solar panels, transponders, antennas, etc.).