public void PostUrl()
        {
            CheckoutShoppingCartRequest Req;
              // Sandbox.
              Req = new CheckoutShoppingCartRequest
            ("123", "456", EnvironmentType.Sandbox, "USD", 0);
              Assert.AreEqual("https://sandbox.google.com/checkout/api/checkout/v2/merchantCheckout/Merchant/123", Req.GetPostUrl());
              Req = new CheckoutShoppingCartRequest
            ("123", "456", EnvironmentType.Production, "USD", 0);
              Assert.AreEqual("https://checkout.google.com/api/checkout/v2/merchantCheckout/Merchant/123", Req.GetPostUrl());

              Req = new CheckoutShoppingCartRequest
            ("123", "456", EnvironmentType.Sandbox, "USD", 0, true);
              Assert.AreEqual("https://sandbox.google.com/checkout/api/checkout/v2/merchantCheckout/Donations/123", Req.GetPostUrl());

              Req = new CheckoutShoppingCartRequest
            ("123", "456", EnvironmentType.Production, "USD", 0, true);
              Assert.AreEqual("https://checkout.google.com/api/checkout/v2/merchantCheckout/Donations/123", Req.GetPostUrl());
        }