public void AcceptPurchaseOrderProcessed() { decimal total = 48.5m; int customerId = 4567890; FakePurchaseOrderProcessor orderProcessor = new FakePurchaseOrderProcessor(); List <IItemLine> itemLines = new List <IItemLine> { new ItemLine { Description = "Book Club Membership", Type = ItemLineType.Membership } }; IPurchaseOrder po = PurchaseOrder.Create(orderProcessor, total, customerId, itemLines); po.Accept(); orderProcessor.ProcessedOrders.Any(pId => pId == po.Id).ShouldBeTrue(); }