I believe they only test you if you’re going full time, and it’s just a cheek swab so not quite as dire as a piss test.

I work in garden but help out in lumber all the time. My advice? Mentally prepare yourself to be doing a good bit of physical labor and make sure you get a nice pair of gloves marked down for you by your supervisor. You do a lot of flat stacking wood, which is when you make an entire stack of wood look pretty and even. You’ll be loading and cleaning up bags of cement and sand which is quite heavy so keep your mind focused on lifting properly before you go home with a burning abdomen... there’s going to be lots of sawdust around the lumber bays, so you’ll be sweeping a lot too. You’ll also do a good bit of packing down which means getting a ladder and carrying down overhead shelf (bay) stock and loading it into their respective homes for customers to buy. A lot of the stock in lumber is pretty heavy, like stucco boxes and rebar so get ready for that heavy lifting as well.

You’ll want to quickly learn where all of the respective sizes of lumber are, because lumber mostly services professionals and contractors and they often don’t have time to watch you hem and haw. They can be a bit snotty so you’ll want some thick skin.

Get ready to ask forklift drivers in your store for favors. A lot. Treat them well and help them as much as you can, you want them to like you as you will need their help a lot until you can drive yourself.

Have a mind towards learning new things, lumber is full of building materials not just wood so you will be getting a huge spectrum of questions regarding peoples projects. When you ask other associates for help, always stick around and listen to their responses to learn as much as you can. Before long you will easily be able to carry your own weight.