Because their use is not common compared to recs, and because the tests are expensive, most employers will not test for steroids.
I was in a police academy a long time ago, and they didn't test for steroids, although I heard they would if they suspected you of it. It seems that in most agencies, once you are in you can do whatever you want.
My ex GF became an LE officer; she says many of the guys do coke while partying on the weekend and sometimes drink and drive.
We didn't talk about AAS, but if they don't worry about recs, I highly doubt they worry about AAS.
I have heard that NYPD is getting more keen to the whole AAS thing, but I that is just something I heard.
I think CO's are tested far more strictly with drug related stuff because that is how most drugs get into prisons/jails.