Finish first four tests: initialize,status available,checked out-pass,checked out-fail
Finish first six tests: book checkin, borrower name
Finish first eight tests: create lib (with books as Array), add book
Finish first ten tests: add multiple books, check out by id
Finish first 13 tests: know who borrowed a book, doesn't allow checkout twice, allows check-in
Finish 17 tests: checkout limit, returns available books, allows re-check out, returns borrowed books