How to mock a Stream response when calling HttpClient GetStreamAsync

Question

I'm trying to test a class that uses HttpClient and i have to fake the Stream response.

This is the code i'm trying to test.

            try
            {
                _httpClient.Timeout = TimeSpan.FromMinutes(10);
                _httpClient.BaseAddress = new Uri(BaseAddress);
                _httpClient.DefaultRequestHeaders.Accept.Clear();
                _httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
                _httpClient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Basic", _credentials);

                using (Stream s = _httpClient.GetStreamAsync(API_string).Result)  <---- this is the trouble line.
                using (StreamReader sr = new StreamReader(s))
                using (JsonReader reader = new JsonTextReader(sr))
                {
                    JsonSerializer serializer = new JsonSerializer();

                    return serializer.Deserialize<T>(reader); //breaks loop
                }
            }

From the test side, i can insert my custom HttpClientHandler and send back any response i want.

This is my Fake HttpClientHandler builder (I'm using Moq).

    public HttpClientHandler MockHttpClientHandler()
    {
        var requestUri = new Uri("Uri.Expected.To.Be.Called");
        var expectedResponse = "Response text"; <-- This is where i need to write the Object to be returned.

        var mockResponse = new HttpResponseMessage(HttpStatusCode.OK) { Content = new StringContent(expectedResponse) };
        var mockHandler = new Mock<HttpClientHandler>();
        mockHandler
            .Protected()
            .Setup<Task<HttpResponseMessage>>(
                "SendAsync",
                ItExpr.Is<HttpRequestMessage>(message => message.RequestUri == requestUri),
                // ItExpr.IsAny<HttpRequestMessage>(),
                ItExpr.IsAny<CancellationToken>())
            .Returns(Task.FromResult(mockResponse));

        return mockHandler.Object;
    }

My test breaks when it tries to run the return line, because whatever i'm sending back can't be deserialized. I just don't know what my Stream s should look like, and i can't see its contents by debugging either.

I'm fairly lost here. Maybe my approach is wrong?

Thanks for any help you can give me.

Answer 1

        var stream = new MemoryStream();

        var httpResponse = new HttpResponseMessage
        {
            StatusCode = HttpStatusCode.OK,
            Content = new StreamContent(stream)
        };

        var handlerMock = new Mock<HttpMessageHandler>();
        handlerMock
            .Protected()
            .Setup<Task<HttpResponseMessage>>(
                  "SendAsync",
                  ItExpr.IsAny<HttpRequestMessage>(),
                  ItExpr.IsAny<CancellationToken>())
           .ReturnsAsync(httpResponse);