public async Task TestShouldCreateBillUSD()
        {
            List <Item> items = new List <Item>();

            items.Add(new Item()
            {
                Price = 30.0, Quantity = 9, Description = "product-a"
            });
            items.Add(new Item()
            {
                Price = 14.0, Quantity = 16, Description = "product-b"
            });
            items.Add(new Item()
            {
                Price = 3.90, Quantity = 42, Description = "product-c"
            });
            items.Add(new Item()
            {
                Price = 6.99, Quantity = 12, Description = "product-d"
            });

            // create a bill and make sure we receive an id - which means it has been successfully submitted
            var bill = new Bill()
            {
                Number   = "1",
                Currency = Currency.USD,
                Email    = "", //email address mandatory
                Items    = items
            };
            var basicBill = await _bitpay.CreateBill(bill);

            Assert.IsNotNull(basicBill.Id);
        }