I had to take several tests a few months ago and the swabs seem dry. Also, it's up to you how thoroughly you want to swab yourself. It wouldn't be a reliable way to expose people to a substance.

I think the rumor that sticking the swab deeply and irritating your membranes actually causes positive test results has a lot of merit. That was my experience (anecdotal, but still.) I also think the nurses who run the test manipulate the results based on the chart you fill out for them. You have to tell them your symptoms, whether you've had contact with someone with Covid, whether you've already had a positive test, and how long you've had symptoms. They don't just neutrally administer tests.