def test_book_cannot_return_book_if_not_checked_out():
book = Book('TITLE', 'DESCRIPTION', 'ISBN')
book.check_in('BORROWER')
def test_book_cannot_return_book_if_not_borrower():
book = Book('TITLE', 'DESCRIPTION', 'ISBN')
book.check_out('BORROWER')
book.check_in('ANOTHER BORROWER')
