I graduated a few years ago, so fairly recent. Big Ten Conference school, we were tested once every single year, maybe twice one of the years. I'm pretty sure those tests were done by the conference, not NCAA. NCAA doesn't test EVERY school all of the time. I believe each conference has their own testers and they can differ on how often they test. So I was tested every year once or twice in Big Ten, but I've spoken with Big 12 people and they were only twice all of college.
And then at the Big Ten championships there was 'random' drug testing, but it was more like random testing for people that finished in the top 3. Same sort of thing at NCAA's, 'random' but only for a percentage of the people that placed high.
We've had multiple people have to sit out from smoking weed as a result of the Big Ten drug testing. It seemed it was only a few meets at the beginning of the year for a first-offense. If it happened three times or maybe even twice, they were off the team.