Hi, I assume you are talking about a test you buy at the drugstore? Did you get a positive or a negative? If you got a positive, I'd say it was accurate. If you got a negative, I assume you know for sure that the guy did not fake his swab?
Then I'd say you don't have anything to worry about. If you ever need to file for child support, you will have to re-test with a lab certified by the family courts in your area for legally determining paternity, but it sounds good.
Take another test if you cannot believe one test. Just don't then ask yourself if that test is also wrong. :)