Random and Scheduled are Two Different Things, Right?

The horror of the Amish school shootings is too much to process, so I'm nitpicking the AP story. (I've already heard from people who had TVs on today that the coverage was predictably awful, with helicopters and newsvans invading the Amish community. If only they could give the same attention to, say, bills that gut our Constitution. But I digress.)

Anyway, I was reading the AP story and came across this section:

Miller said that Roberts had been scheduled to take a random drug test on Monday. But the officer said it was not clear what role that may have played in the attack.

Scheduled to take a random drug test? How does that work?