public void DownloadInvoice(bool isValidBan, bool isValidInvoiceNumber)
        {
            //// Arrange
            var ban           = GetBanStr(isValidBan);
            var invoiceNumber = GetInvoiceNumber(isValidInvoiceNumber);

            // pdfStream == null
            // Error(HttpStatusCode.NotFound.ToString(), ErrorCode.InvoiceNotFound

            // catch (HttpRequestException ex)
            // new Error(HttpStatusCode.NotFound.ToString(), ErrorCode.InternalServerError

            //// Act
            var result = _controller.DownloadInvoice(ban, invoiceNumber);

            //// Assert
            Assert.IsNotNull(result);
        }