VR Headset Simulator

Is it possible to code a program for HoloLens or Oculus Rift or HTC Vice? And is there a simulator for a VR headset like HoloLens or Oculus Rift or HTC Vice to experiment the code with if you don’t have a VR Headset?

There is an VR Simulator on the Assetstore. It only works for XR Input based projects though.
Here is a link: VR Simulator | Input Management | Unity Asset Store