Extensions for Mock<IHttpClientFactory> that help setup the HttpClient with fake response content

HttpMocking.cs

using Moq;
using System;
using System.Net.Http;

namespace Example.Testing
{
    public static class HttpMocking
    {
        public static void SetupHttpClient(this Mock<IHttpClientFactory> httpClientFactory, string response = "")
        {
            var handler = new MockMessageHandler(request =>
            {
                return new HttpResponseMessage(System.Net.HttpStatusCode.OK)
                {
                    Content = new StringContent(response)
                };
            });
            SetupHttpClient(httpClientFactory, handler);
        }

        public static void SetupHttpClient(this Mock<IHttpClientFactory> httpClientFactory, Uri expectedUrl, string response)
        {
            var handler = new MockMessageHandler(request =>
            {
                if (request.RequestUri != expectedUrl)
                    throw new Exception("Wrong URI for HttpClient"
                        + $"\n Expected: {expectedUrl}"
                        + $"\n Actual:   {request.RequestUri}");
                return new HttpResponseMessage(System.Net.HttpStatusCode.OK)
                {
                    Content = new StringContent(response)
                };
            });
            SetupHttpClient(httpClientFactory, handler);
        }

        public static void SetupHttpClient(this Mock<IHttpClientFactory> httpClientFactory, string expectedUrl, string response)
        {
            SetupHttpClient(httpClientFactory, new Uri(expectedUrl), response);
        }

        private static void SetupHttpClient(Mock<IHttpClientFactory> httpClientFactory, MockMessageHandler handler)
        {
            var client = new HttpClient(handler);
            httpClientFactory.Setup(f => f.CreateClient(It.IsAny<string>()))
                .Returns(client);
        }
    }
}

MockMessageHandler.cs

using System;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;

namespace Example.Testing
{
    /// <summary>
    /// HttpClient cannot be mocked, but the message handler can be replaced
    /// See https://github.com/aspnet/HttpClientFactory/issues/67
    /// </summary>
    public class MockMessageHandler : HttpMessageHandler
    {
        private Func<HttpRequestMessage, HttpResponseMessage> _handler;

        public MockMessageHandler(Func<HttpRequestMessage, HttpResponseMessage> handler)
        {
            _handler = handler;
        }

        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            return Task.FromResult(_handler(request));
        }
    }
}