public void BillWithNonGroseryItems()
        {
            //act
            _billingService.AddItem(new OtherItem {
                Name = "Laptop", Price = 50000
            });
            _billingService.AddItem(new OtherItem {
                Name = "Mobile", Price = 20000
            });

            var result = _billingService.GetBillDetails();

            //assert
            Assert.AreEqual(result.TotalAmount, 70000.00m);
            Assert.AreEqual(result.TotalDiscount, 3500.00m);
            Assert.AreEqual(result.TotalAmount - result.TotalDiscount, 66500.00m);
            Assert.AreEqual(result.BillDiscount, 3500.00m);
            Assert.AreEqual(result.TotalBill, 63000.00m);
        }