Suppose you have written a testing program, to be used in a classroom.
How would you enforce the participants don't use any other software (no Internet, no calculator, no console etc.) during the exam time? Something similiar to "testing mode" in one of TI calculators.
Another possible application: lock players during a chess/bridge computer tournament.
Raymond Chen would recommend asking "What if Two Programs Did This?"... that is, what would happen if you had two such programs running at the same time? If the resulting scenario doesn't make sense, you may want to rethink your design.
That being said, if the students are taking the test on computers you (or your IT department) have control over, I think it would be much easier to make a special StudentTest account that only has permissions to run is the testing software, and is denied access to everything else. That way your testing software isn't 5% test, 95% attempt to keep the student from cheating which probably will have a hole in it at some point anyway.
This is a common Windows programming problem. Do a Google search for "windows kiosk mode".