It is very common in my experience. Google, Microsoft, Apple, and every tech company I've ever applied to (even small midwestern shops) do not drug test.
The FBI has a problem hiring good security experts because of their strict drug testing policies.
I heard through the grapevine that one of my employers (who drug tested at time of hire, but not after that) said "I can't do random testing, I'd lose half my staff."
Another one joked that "We used to drug test at hire, and if you didn't come up positive for ANYTHING, we'd fire you." That was based in a state where medical MJ is legal, and their drug policy was the most reasonable I'd ever seen. "What you do on your own time is your business, and we only start caring if it affects your work performance or interactions with coworkers during work hours."
Meanwhile, the place where I spent 12 years not only tested at hire, you were under the constant "threat" of "random" testing, and the same policies applied to everyone - from rig workers and truck drivers, to programmers. The only time I got "randomly" tested was after a coworker on my team had blown his "random" test... A couple of weeks later I was "randomly" selected; at least HR had a sense of humor about it. "You won the piss test lottery! Go down to XYZ as soon as you get in this morning and pee in a jar..."
This meant that my first and only time I've ever tried MJ was at the age of 40.
I have personally experienced a drug test with a technology company for a pre-employment screening, and heard of others that do the same. The company gave ample notice, but I don't think it's fair to paint a picture where drug tests are non-existent within tech.