yep, you're absolutely right. You can get 100% testing coverage when you define it as "percentage of code executed when tests are run".
That said... that kind of coverage isn't quite as useless as it might seem. If your tests do execute every line, even in a completely contrived way, you will catch a lot if you change your code. You just tend to catch more of the "wrong number of arguments passed to a method" kind of error than "you are allowing the autopilot to try to land the plane 100 feet below the runway" kind of error ;)
Careful though with tests that literally execute every line of code: You tie your test to your implementation. That makes even the slightest refactoring difficult. Better to have unit tests that only care about the functional interface.
That said... that kind of coverage isn't quite as useless as it might seem. If your tests do execute every line, even in a completely contrived way, you will catch a lot if you change your code. You just tend to catch more of the "wrong number of arguments passed to a method" kind of error than "you are allowing the autopilot to try to land the plane 100 feet below the runway" kind of error ;)