X-Plane is incredibly extensible. You can simulate new aircraft, make 3-D models, or even change the functionality of the program in drastic ways.
As a developer, you’ll (hopefully) want your products to be VR compatible. To do so, you can of course use a real headset. If the need for debugging arises, that may not be very practical.
So, here’s how to fake VR in X-Plane: