I dont know if id want to take a drug test that the other fighter is pushing on me. Id be annoyed by that and say no out of principal. I feel like he is my opponent and im not going to do something just because he wants me to. (My stubbornness gets the best of me sometimes)
That said if my boss asked me to agree with the Vada testing then i wouldnt mind. Or if it was a "Fight isnt going to happen unless i take the test" scenario.
But if both people signed the contract and then my opponent started throwing out the "Hey go get tested" comments. I probably would just reply with a simple short insult.
Oh and if they had 2 more rounds its likely Nelsons chin would have separated itself from Nelsons head and got out of there. Maybe it would have flipped Nelson the bird on its way out.