It depends on how much it is bleeding. I'm typically most suspicious of dark reds and blues, you can dunk a piece in to a coffee cup with a white inside, fill with hot/boiling water, swish around with a fork, and see if the water changes color or not. If it's just a little, nothing to worry about. If it looks like you can dye an egg... well then that's bad and we'll have to take you through it. Other ways to test, you can dampen a corner of the fabric and rub it on a white paper towel as well and see if there is cast off, but that usually results in those little crumbles of paper fiber.
I very rarely buy precuts but I do buy a lot of bags of yardage at the thrift store and so I'm often washing/testing small pieces. If it is fat quarter or above and I feel relatively confident about it, I just put it in with like colored normal laundry. Smaller I put into lingerie bags.
I don't think I could stand to wash a thing of jellyroll strips... but I'm pretty sure we have people here who at least dunk them.