Do you need an Oculus, HTC Vive, or Valve Index to test it?

I’m trying to code a VR game for my friend and I don’t have a VR system. I don’t want to buy one so, can someone answer this question?

You can use/make some kind of VR emulator. Using this you can test many things, but probably not all. Especially game feel and special interactions are hard to get right with the emulator