This wouldn't be the first time when Darkseid is rumored to be the great villain to unite the Justice League. And, until next year when we'll get a clear look at the DC Movie Universe, this won't be the last time.
But this new rumor doesn't say that it will be the ruler of Apokolips to test the superheroes for the first time. Instead, Darkseid will send one of his generals ahead, to see the level of power possessed by the Earthlings.
Darkseid's son

This whole rumor is sparked by the above pic, released by Zack Snyder (one of the first pics we've got from the set of Batman v Superman). But what does it have to do with Darkseid?
According to this rumor, that isn't a lightsaber held by Superman. Instead, it is the Beta Club, owned by Kalibak. And who is this Kalibak? Well, he is the oldest son of Darkseid.
So, apparently, the major villain of Batman v Superman won't be Doomsday, just like it won't be Darkseid himself. Instead, it will be another resident of Apokolips, sent ahead to scout the planet.

