How to pass in a mocked HttpClient in a .NET test?

Question

I have a service which uses Microsoft.Net.Http to retrieve some Json data. Great!

Of course, I don't want my unit test hitting the actual server (otherwise, that's an integration test).

Here's my service ctor (which uses dependency injection...)

public Foo(string name, HttpClient httpClient = null)
{
...
}

I'm not sure how I can mock this with ... say .. Moq or FakeItEasy.

I want to make sure that when my service calls GetAsync or PostAsync .. then i can fake those calls.

Any suggestions how I can do that?

I'm -hoping- i don't need to make my own Wrapper .. cause that's crap :( Microsoft can't have made an oversight with this, right?

(yes, it's easy to make wrappers .. i've done them before ... but it's the point!)

Answer 1

You can replace the core HttpMessageHandler with a fake one. Something that looks like this...

public class FakeResponseHandler : DelegatingHandler
    {
        private readonly Dictionary<Uri, HttpResponseMessage> _FakeResponses = new Dictionary<Uri, HttpResponseMessage>(); 

        public void AddFakeResponse(Uri uri, HttpResponseMessage responseMessage)
        {
                _FakeResponses.Add(uri,responseMessage);
        }

        protected async override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
        {
            if (_FakeResponses.ContainsKey(request.RequestUri))
            {
                return _FakeResponses[request.RequestUri];
            }
            else
            {
                return new HttpResponseMessage(HttpStatusCode.NotFound) { RequestMessage = request};
            }

        }
    }

and then you can create a client that will use the fake handler.

var fakeResponseHandler = new FakeResponseHandler();
fakeResponseHandler.AddFakeResponse(new Uri("http://example.org/test"), new HttpResponseMessage(HttpStatusCode.OK));

var httpClient = new HttpClient(fakeResponseHandler);

var response1 = await httpClient.GetAsync("http://example.org/notthere");
var response2 = await httpClient.GetAsync("http://example.org/test");

Assert.Equal(response1.StatusCode,HttpStatusCode.NotFound);
Assert.Equal(response2.StatusCode, HttpStatusCode.OK);