Pin parking_fee before the new ticket machines

New ticket machines go in next month, and they will run a port of this function. The old machines are the spec.

Your task

Pin what parking_fee does today. Not what the price board says. 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. Write it for the next engineer

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