public void CanBorrowBook() { Book myBook = new Book("Cash Craig", "Fake Book", 1991, 7); int oldCount = myBook.AvailableAmount; Borrowable bookBorrowable = new Borrowable(null, new Borrow(myBook)); bookBorrowable.BorrowOne(); int newCount = myBook.AvailableAmount; Assert.AreEqual(oldCount - 1, newCount); }