Guys, don't panic... there is a BIG reason this could be happening and it might not be anything to do with Brock.
Recently there have been a number of high profile cases of "failed tests" that have basically had to be let go or have led to VERY flimsy bans. In Tennis, Maria Sharapova was banned despite using a substance, medically cleared for ten years. Stopping it's use would have ended her career, arguably she made that decision to continue but it is at best a weak case on WADA's part, you know this when Nike DON'T end their sponsorship of her cos of the ban...normally they'd jump ship immediately.
In Football it's even worse, a UK second tier player was flagged for using an inhaler when he had an apparent first time astmha attack. The inhaler wasn't his but he was flagged as failing, despite there being a diagnosis very shortly after. He didn't get a ban, but was "severely reprimanded", while WADA pushed for a ban...
Then the curious case of Mamadou Sakho of my team Liverpool. He was "flagged" and provisionally suspeneded after an alleged failiure, which took him out of the two biggest games of the season and arguably cost us at least one trophy. It transpires he ASKED for the provisional 30 day suspension which then ended with no outcome seemingly, but he wasn't selected for France in their Euro 2016 squad because of it. Just last week, a full 2 months after the test, they finally cleared him and WADA didn't even show up to the hearing. It basically transpired that what he had used was not actually on the banned list, WADA felt it should be and wanted to retrospectively apply the ban. Sakho is now in the situation where he has a strong legal case to sue both WADA and Uefa, while WADA are almost obliged to appeal the decision, lest they look even more incompetent than they do.
This is an "easy win" for WADA on paper. if there is a steroid in there then their credibility is quickly "restored". If as I suspect, this is the same fat burner as Sakho may have used then it is a different kettle of fish as they may have only VERY recently updated their rules or be in the process of doing so. It smells to me like this is a WADA thing, they lost Sakho so they want SOMEONE... and Lesnar is an easy target as people will assume it's roid related and Vince will probably accept it to keep damage to his business to a minimum.
It could be a big mistake on WADA's part... as this opens up the whole "why are WWE guys tested" when their counterparts in Hollywood are not required to be. Brock, yes, he put his head above the parapet by going into UFC... but a Cena, Triple H, Neville, Rollins, all those guys who "could be juicing" have had injuries that would cover steroid use and ultimately they are actors... They're NOT in a competitive sport, and no one comments if Arnie/Sly/Dwayne juice for a movie role....