Ignore the retard above me, everyone is on some kinda shit or a higher test dose than TRT at least.
Until you reach Pro level (Pro is just any paid fight at any promotion, not necessarily the major leagues) it doesn't fuckin matter. Ammys get a basic bloodborne pathogen panel just to make sure you're not gonna get the other guy or a ref sick if you gush all over em. Nobody fuckin pays to get ammy fighters tested for all WADA/USADA banned substances. All the guys I met when I was in the ammy/pro-am circuit ran Test, Var/Tbol, some ran Deca, toward the end of my time SARMs came around so some retards started hopping on GW50156 or w/e the numbers are and MK677 was apparently gaining popularity for guys going up a class and for general recovery.
When you take the leap and are being paid for your fights, it is 100% up to the promoter whether they test or not. Most don't, but if you get scouted by a big league they're gonna have you tested for sure so if you end up with a respectable record you need to hook up with a coach that understands how to time your drugs so you don't get popped.
Beyond the pro-am/ammy circuits I can't give you any more info. The most 'famous' guys I worked with or fought went up to Bellator except one who was a top wrestler HS/Collegiate who transitioned to MMA and he got taken by a promoter out in Thailand. Bellator testing is real, or was in 2014ish from what I was told by those guys, and out in Thailand the promoters gave no fucks at all.
I'm gonna be honest: The drugs we take for bodybuilding, powerlifting, strongman and the doses used for these are NOT very compatible with MMA, Boxing, Wrestling, Jujitsu. The only ones worth taking are ones I mentioned above as you're not going to wreck your joints on Test+Deca+Var/Tbol and they're good for helping you maintain your body more than anything. Once you get serious, the training is going to be intense and you'll be unintentionally cutting pretty fast unless you're smashing a shit ton of mcdonalds.
Drugs will help reduce the loss of muscle mass and will work to help strengthen your body in a practical manner as it relates to the muscle functions for the sport. No, it is not gonna make you punch and kick hard as shit but it will help build up the muscular strength of the main movers and stabilizers throughout each motion so you're better built to perform. Shoulders and hips on guys who cycle did not get blown out nearly as often as those who stayed natty and I'd attribute that to the stabilizers being built to supra-physiological levels thanks to the gear. So as to say- A guy who has a 1000lb squat can push kick you really hard, but if he has not built the strength in the muscles that support his leg through that movement then he's not going to be delivering many of those kicks. Apply this ideology to everything you do- You're going to 'bulletproof' (I hate that buzzword term but it works) yourself to keep you in the game longer. Also a lot of guys swore by things like the glute bridge with weight since it mimics bucking someone out of mount but that only applies from that specific position- Using gear and training will help strengthen your hips, legs and core to work positions from unorthodox or suboptimal positions as opposed to one specific A-B movement pattern.
All this write-up to say, don't just blast gear assuming that if you go in on 6g of Tren and Test with a few Halo tabs pre-fight it'll make you Superman. If that's your perspective of gear in relation to fighting, I hope this does a lot to help change your mind. Good luck and remember the most vicious fighters are in the promotions nobody has heard about yet. The guys in the UFC are on top of the mountain- Ammy and Pro-am guys are fucking HUNGRY bro. Last I checked in with my old coaches and some of the guys from those days, I heard a slew of stories about names that nobody knew yet but they are definitely going to. Some real fuckin animals out there just waiting to get noticed, and these guys aren't fighting for points.