Hm... that is indeed a weird problem. If you don't get tested on Monday, that is a surprise, because you expect to get tested on Monday. Then if you don't get t

Hm... that is indeed a weird problem. If you don't get tested on Monday, that is a surprise, because you expect to get tested on Monday. Then if you don't get tested on Tuesday, that is surprising, because you've inductively determined that Wednesday through Friday are ineligible. The rest of the days follow the same logic. In effect if you just tell someone "you will have a surprise test next week", that is contradictory, since they can reasonably expect to have a test at any moment during the following week and the test can therefore never be surprising, just the absence of the test.