Pin late_fee before the desk software moves

The library is moving its desk software to a hosted system, and an assistant will port late_fee. Staff quote today's fees to members, so the port has to match them to the cent.

Your task

Pin what late_fee does today. Not what the rules should be. What the code does.

• fill REGRESSION_TESTS with cases: the arguments in, the value it returns today
• a test that expects the RIGHT answer instead of the CURRENT one fails the clean run
• at submit each test runs again against versions of the function with one line changed
• a change your tests do not notice is behavior you left unpinned
• the walk-through is read by the critique, not by the suite, so write it for the next engineer

The suite runs your tests against the untouched code, then against mutations you have not seen.