The craziest part to me is not that you can get fired for using weed on your own time two weeks before due to drug testing, it's that you can get completely drunk the morning of the drug test and still pass it because alcohol doesn't count but weed does.
Depends on the test, of course, but alcohol will show up in your piss for a day or two and many places (particularly ones that test for operating heavy machinery) do care about it.
Alcohol can be detectable for up to 14 days, but mostly only court ordered drug tests will run the test required to detect alcohol that long. If you work for the railroad though, expect hair follicle tests and they will know everything you put in your body.
We shouldn't be at work even with alcohol in our system so... Should something happen and it came out we regularly got inebriated, we'd still be fucked.