public void DeleteCopyOfBookTest()
        {
            AddCopyOfBookTest();
            Assert.AreEqual(5, _dataLayer.GetAllCopiesOfBook().Count());
            CopyOfBook copy = _dataLayer.GetAllCopiesOfBook().First();

            _dataLayer.DeleteCopyOfBook(copy);
            Assert.AreEqual(4, _dataLayer.GetAllCopiesOfBook().Count());
            Assert.IsNull(_dataLayer.GetCopyOfBook(copy.Id));
        }