public IEnumerator TestListCustomPrompts()
        {
            Log.Debug("TextToSpeechServiceV1IntegrationTests", "Attempting to ListCustomPrompts...");
            CustomModel customModel     = null;
            string      customizationId = "";

            service.CreateCustomModel(
                callback: (DetailedResponse <CustomModel> response, IBMError error) =>
            {
                Log.Debug("TextToSpeechServiceV1IntegrationTests", "CreateCustomModel result: {0}", response.Response);
                customModel = response.Result;
                Assert.IsNotNull(customModel);
                Assert.IsNull(error);
                customizationId = customModel.CustomizationId;
            },
                description: "testString",
                name: "testString",
                language: "en-US"
                );

            while (customModel == null)
            {
                yield return(null);
            }

            Prompts prompts = null;

            service.ListCustomPrompts(
                callback: (DetailedResponse <Prompts> response, IBMError error) =>
            {
                Log.Debug("TextToSpeechServiceV1IntegrationTests", "ListCustomPrompts result: {0}", response.Response);
                prompts = response.Result;
                Assert.IsNotNull(prompts);
                Assert.IsNotNull(prompts._Prompts);
                Assert.IsNull(error);
            },
                customizationId: customizationId
                );

            while (prompts == null)
            {
                yield return(null);
            }

            bool isComplete = false;

            service.DeleteCustomModel(
                callback: (DetailedResponse <object> response, IBMError error) =>
            {
                Log.Debug("TextToSpeechServiceV1IntegrationTests", "DeleteCustomModel result: {0}", response.Response);
                Assert.IsTrue(response.StatusCode == 204);
                Assert.IsNull(error);
                isComplete = true;
            },
                customizationId: customizationId
                );

            while (!isComplete)
            {
                yield return(null);
            }
        }