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));
}