I don't know about the nicotine test. They drew blood during surg prep. If they ran the test, they ran it from that. The surgery itself was nothing. I was sore, but not much pain. The only time I used my pain pump was when my back (pinched nerve) hurt so bad from lying in bed and I wanted to go to sleep. My appendectomy 24 years ago was much worse. I was uncomfortable in the left shoulder from the gas, so I was up and walking a few hours after surgery. I didn't want to eat or drink afterwards which made the leak test where you fill up on a liquid miserable, but doable.
With the weight loss since surgery, my back pain has all but disappeared. We moved residence recently and I would not have been able to do that without severe back pain a year or two ago. I would do the surgery again in a heartbeat. My quality of life has greatly improved. You go thru brief phases where you feel regret or depression that you can't eat like everyone else. So expect those, it's just your mind coping with the changes. Think about the benefits your getting. I'm off blood pressure medicine and GERD medicine. It's more than worth it. Best wishes, and good luck!