The quick answer is sometimes. An example is the Canadian duathlete Shari Boyle who did an interesting disappearing act while asked to submit to an out of competition test while doing a track workout (she was at the time under suspension). I hope the following link works:
http://www.cces.ca/...iolationBoyle2-E.pdf And why would she dope? To get ready for her "come back". My guess, however, was this time she wasn't just doing ephedrine. When you actually read the Canadian aribitrator's decisions in regard to this case (and her original suspension) you really have to laugh at how gullible they (arbitrators) are. Must be nice (from a doper's perspective!). For a good laugh go to the website with the full text of her two suspensions - comical, just comical.
http://www.adrsportred.ca/