Ooh, I know the answer to this one! Since you've been with GenX, you don't need to do any kind of tests. Talk to one of the established X-Men - Scott, Jean, Kurt, Garrison, JPC, Logan or Clarice (basically anyone that's not me or Tandy!) about joining, you'll go through the DR run Garrison mentioned above, and that's pretty much it. You do a lot of training on the job, so to speak (I call it a job, but we don't get paid, obvs, beyond living in the fancy mansion with free room and board, it's more like being a volunteer fire fighter) and if there's something you need to know, there's always someone to ask.