There are at least two tests for it, or at least there were in the mid 1990s. One's a quick clinical test with lots of false negatives than can be done in-office but unless it's a campus healthcare clinic at a university they probably don't bother. The other is a more sensitive lab test that takes a few days. If you're having a really serious set of symptoms they may test to confirm it's not something else. If it's a minor case, two weeks of bedrest fix a lot of issues in a young adult and you do probably already have it anyway.