Forgot to mention this in my earlier post, but if it's a big(ger) regional/national company, I'd say absolutely forget it. If it's a small/local outfit, you might get away with admitting to weed, but without reliable "inside" info to that effect beforehand, it's just not worth the risk (ie, any risk of disclosure beyond them, which, however slight/theoretical, is always a possibility to one degree or another.) There's just not enough of an up-side in this case, for a job it doesn't sound like you'd be looking to stay in long-term and only one week into your job-search...
Even if they're a small outfit, if they really "didn't care" for whatever the reason (whether it's true moral/legal opposition, insurance purposes, "public image", or whatever), they wouldn't be testing for it in the first place...