public void SendPrecompiledLetterNotificationGeneratesExpectedRequest()
        {
            JObject expected = new JObject
            {
                { "reference", Constants.fakeNotificationReference },
                { "content", "JVBERi0xLjUgdGVzdHBkZg==" }
            };

            MockRequest(Constants.fakeTemplatePreviewResponseJson,
                        client.SEND_LETTER_NOTIFICATION_URL,
                        AssertValidRequest,
                        HttpMethod.Post,
                        AssertGetExpectedContent, expected.ToString(Formatting.None));

            LetterNotificationResponse response = client.SendPrecompiledLetter(
                Constants.fakeNotificationReference,
                Encoding.UTF8.GetBytes("%PDF-1.5 testpdf")
                );
        }