I use oxygen during the 6 min walk test, as well as, during physical therapy exercise. I don’t use oxygen during the day though.

I have never heard of the 3-minute test. I do, however, certainly know the 6MWT. Not on my list of favourites. I did just look it up and found this article that some of you may want to read.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC31...

The usefulness of submaximal exercise gas exchange to define pulmonary arterial hypertension

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3164909/

Hi All, I do the six min walk test which is okay but I also have to do the three min step test which evaluates sufficient perfusion and cardiac out put. It measures fractions of oxygen and carbon dioxide in expired gas, expired air volume and minute ventilation with a nonrebreathing valve connected to a metabolic cart. They plug your nose and have you breath into a tube and you step up and down on a 12 inch platform to the beat of a metronome for three min with out your oxygen if your on oxygen. I need to have my third one done and an not looking forward to it.

I do the 6 min walk test, had done it for years with rheumatologist as screening long before I was officially diagnosed with the RHC. I can finish it because it's flat, and they use the hallway which means that you have a "break" every few yards before turning. It's not really representative of real world walking with hills so I question its value.

They should provide a wheelchair for you to get there then...or at least you should bring a wheeled walker to help you get there.