Can my employer withhold pay and make me pay back earned wages until I take a drug test?

My employer hired me and told me I would need to pass a drug test along with completing several other training items prior to employment (CPR, bus training, etc.). She hired me last minute and let me begin working without all of the training completed. Over the spam of a few weeks I finished everything and sent her an email asking if I missed anything. She said no and neither of us noticed that the physical/TB test/drug screening had not been completed. I have worked 8.5 hours a day for the last 9 weeks and today received an email that she doesn't have my drug screening results. I let her know it looks like we both forgot and that I hadn't done them. She told me to do them ASAP (but I don't have time until next week because of the hours I work) and that she will withhold my pay until it is completed and I pass. She said if I fail I will owe them past wages. I think I will pass, but there is no way this is legal, right?