This is a fragile test that will eventually fail on a particularly rainy day. It's what we call a flickering test.

I'm guessing you picked the number 5 arbitrarily because you saw the number of threads increase. Why has the number of threads increased by 5? Maybe because `Timeout` creates a new executor every time `timeout()` is called. Try making the executor a private static field so there is only ever one, then see if you can get the thread difference down to 1.