FakeResponseHandler.cs

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

UnitTestInjectionExample.cs

[TestClass]
public class UnitTest1
{
    public UnityContainer Container { get; set; }

    [TestInitialize]
    public void Setup()
    {
        Container = new UnityContainer();

        var fakeResponseHandler = new FakeResponseHandler();
        fakeResponseHandler.AddFakeResponse(
                new Uri("http://example.org/api/restserviceexample/1"),
                new HttpResponseMessage(HttpStatusCode.OK)
                {
                    Content = new ObjectContent<ExampleDto>(new ExampleDto 
                    {
                        Id = 1,
                        Name = "Printer"
                    }, new JsonMediaTypeFormatter())
                });


        Container.RegisterType<Proxy, Proxy>();

        Container.RegisterType<HttpClient>(
             new InjectionFactory(x =>
                  new HttpClient(fakeResponseHandler) { BaseAddress = new Uri("http://example.org/") }
             )
        );
    }

    [TestMethod]
    public void TestProxy1()
    {
        var proxy = Container.Resolve<Proxy>();

        var response = proxy.GetExample(1).Result;

        Assert.IsNotNull(response);
        Assert.AreEqual("Printer", response.Name);
    }
}