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)); }