When are boxers tested for steroid and other drug use? After or before their fight? And since boxing is international sport how do boxing commissions (WBO WBC IBF etc) regulate this problem around the globe?

Here in California we've heard of Vargas testing positive after the DLH fight, Mosley's name has been out there in reports. With the baseball report out today it makes us boxing question steroid use in boxing. Is it a hush hush issue??