How to Mock HTTPClient from IHttpClientFactory combined with Polly policies in .NET Core using Moq

Question

I create a HTTP Client using IHttpClientFactory and attach a Polly policy (requires Microsoft.Extensions.Http.Polly) as follows:

using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.DependencyInjection;

IHost host = new HostBuilder()
    .ConfigureServices((hostingContext, services) =>
    {
        services.AddHttpClient("TestClient", client =>
        {
            client.DefaultRequestHeaders.Add("Authorization", $"Bearer {accessToken}");
            client.DefaultRequestHeaders.Accept.Clear();
            client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        })
        .AddPolicyHandler(PollyPolicies.HttpResponsePolicies(
            arg1, 
            arg2,
            arg3));
    })
    .Build();

IHttpClientFactory httpClientFactory = host.Services.GetRequiredService<IHttpClientFactory>();

HttpClient httpClient = httpClientFactory.CreateClient("TestClient");

How can I mock this HTTP Client using Moq?

EDIT: Mock means to be able to mock the requests of the HTTP. The policy should be applied as defined.

Answer 1

As described in many other posts on stackoverflow you don't mock the HTTP Client itself but HttpMessageHandler:

Mock<HttpMessageHandler> handlerMock = new Mock<HttpMessageHandler>(MockBehavior.Strict);
handlerMock
    .Protected()
    .Setup<Task<HttpResponseMessage>>(
        "SendAsync",
        ItExpr.IsAny<HttpRequestMessage>(),
        ItExpr.IsAny<CancellationToken>()
    )
    .ReturnsAsync(new HttpResponseMessage()
    {
        StatusCode = HttpStatusCode.OK,
        Content = new StringContent(response)
    });

To then in the end have a HTTP Client with the mocked HttpMessageHandler as well as the Polly Policy you can do the following:

IServiceCollection services = new ServiceCollection();
services.AddHttpClient("TestClient")
    .AddPolicyHandler(PollyPolicies.HttpResponsePolicies(arg1, arg2, arg3))
    .ConfigurePrimaryHttpMessageHandler(() => handlerMock.Object);

HttpClient httpClient =
    services
        .BuildServiceProvider()
        .GetRequiredService<IHttpClientFactory>()
        .CreateClient("TestClient");