如果您不介意运行自己的http服务器，可以尝试Xim。其实很简单:

using Xim.Simulators.Api;

[Test]
public async Task TestHttpGetMethod()
{
    using var simulation = Simulation.Create();
    using var api = simulation
        .AddApi()
        .AddHandler("GET /books/1234", ApiResponse.Ok())
        .Build();
    await api.StartAsync();
    var httpClient = new HttpClient();

    var response = await httpClient.SendAsync(new HttpRequestMessage(HttpMethod.Get, $"{api.Location}/books/1234"));

    Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);
    Assert.IsTrue(api.ReceivedApiCalls.Any(call => call.Action == "GET /books/1234"));
}

这是使用模拟的一个很好的替代方案，可能适合您在某些场景中的需求。它建立在Kestrel的基础上(是的，我是作者)。

HttpClient的可扩展性在于传递给构造函数的HttpMessageHandler。它的目的是允许特定于平台的实现，但您也可以模拟它。不需要为HttpClient创建装饰器包装。

如果你更喜欢DSL而不是使用Moq，我在GitHub/Nuget上有一个库，它可以让事情变得更容易一些:https://github.com/richardszalay/mockhttp

Nuget包RichardSzalay。MockHttp可以在这里找到。

var mockHttp = new MockHttpMessageHandler();

// Setup a respond for the user api (including a wildcard in the URL)
mockHttp.When("http://localhost/api/user/*")
        .Respond("application/json", "{'name' : 'Test McGee'}"); // Respond with JSON

// Inject the handler or client into your application code
var client = new HttpClient(mockHttp);

var response = await client.GetAsync("http://localhost/api/user/1234");
// or without async: var response = client.GetAsync("http://localhost/api/user/1234").Result;

var json = await response.Content.ReadAsStringAsync();

// No network connection required
Console.Write(json); // {'name' : 'Test McGee'}

加入这个派对有点晚了，但我喜欢在带有下游REST依赖的dotnet核心微服务的集成测试中尽可能使用wiremocking (https://github.com/WireMock-Net/WireMock.Net)。

通过实现一个扩展IHttpClientFactory的TestHttpClientFactory，我们可以重写这个方法

HttpClient CreateClient(字符串名称)

所以当你在应用中使用命名客户端时，你可以控制返回一个连接到你的wiremock的HttpClient。

这种方法的好处是，您不会更改正在测试的应用程序中的任何内容，并且允许课程集成测试对您的服务执行实际的REST请求，并模拟实际下游请求应该返回的json(或任何东西)。这将导致在应用程序中进行简洁的测试和尽可能少的模拟。

    public class TestHttpClientFactory : IHttpClientFactory 
{
    public HttpClient CreateClient(string name)
    {
        var httpClient = new HttpClient
        {
            BaseAddress = new Uri(G.Config.Get<string>($"App:Endpoints:{name}"))
            // G.Config is our singleton config access, so the endpoint 
            // to the running wiremock is used in the test
        };
        return httpClient;
    }
}

and

// in bootstrap of your Microservice
IHttpClientFactory factory = new TestHttpClientFactory();
container.Register<IHttpClientFactory>(factory);

您的接口公开了具体的HttpClient类，因此任何使用该接口的类都被绑定到它，这意味着它不能被模拟。

HttpClient不继承任何接口，所以你必须自己编写。我建议使用类似装饰器的图案:

public interface IHttpHandler
{
    HttpResponseMessage Get(string url);
    HttpResponseMessage Post(string url, HttpContent content);
    Task<HttpResponseMessage> GetAsync(string url);
    Task<HttpResponseMessage> PostAsync(string url, HttpContent content);
}

你的类看起来是这样的:

public class HttpClientHandler : IHttpHandler
{
    private HttpClient _client = new HttpClient();

    public HttpResponseMessage Get(string url)
    {
        return GetAsync(url).Result;
    }

    public HttpResponseMessage Post(string url, HttpContent content)
    {
        return PostAsync(url, content).Result;
    }

    public async Task<HttpResponseMessage> GetAsync(string url)
    {
        return await _client.GetAsync(url);
    }

    public async Task<HttpResponseMessage> PostAsync(string url, HttpContent content)
    {
        return await _client.PostAsync(url, content);
    }
}

所有这些的重点是HttpClientHandler创建了它自己的HttpClient，然后你当然可以创建多个以不同方式实现IHttpHandler的类。

这种方法的主要问题是，你实际上是在编写一个只调用另一个类中的方法的类，然而你可以创建一个从HttpClient继承的类(参见Nkosi的例子，这是一个比我的方法更好的方法)。如果HttpClient有一个可以模拟的接口，事情会简单得多，不幸的是它没有。

This example is not the golden ticket however. IHttpHandler still relies on HttpResponseMessage, which belongs to System.Net.Http namespace, therefore if you do need other implementations other than HttpClient, you will have to perform some kind of mapping to convert their responses into HttpResponseMessage objects. This of course is only a problem if you need to use multiple implementations of IHttpHandler but it doesn't look like you do so it's not the end of the world, but it's something to think about.

无论如何，您可以简单地模拟IHttpHandler，而不必担心具体的HttpClient类，因为它已经被抽象掉了。

我建议测试非异步方法，因为这些方法仍然调用异步方法，但不必担心单元测试异步方法的麻烦，参见这里

这里有一个简单的解决方法，对我来说很有效。

使用moq mock库。

// ARRANGE
var handlerMock = new Mock<HttpMessageHandler>(MockBehavior.Strict);
handlerMock
   .Protected()
   // Setup the PROTECTED method to mock
   .Setup<Task<HttpResponseMessage>>(
      "SendAsync",
      ItExpr.IsAny<HttpRequestMessage>(),
      ItExpr.IsAny<CancellationToken>()
   )
   // prepare the expected response of the mocked http call
   .ReturnsAsync(new HttpResponseMessage()
   {
      StatusCode = HttpStatusCode.OK,
      Content = new StringContent("[{'id':1,'value':'1'}]"),
   })
   .Verifiable();

// use real http client with mocked handler here
var httpClient = new HttpClient(handlerMock.Object)
{
   BaseAddress = new Uri("http://test.com/"),
};

var subjectUnderTest = new MyTestClass(httpClient);

// ACT
var result = await subjectUnderTest
   .GetSomethingRemoteAsync('api/test/whatever');

// ASSERT
result.Should().NotBeNull(); // this is fluent assertions here...
result.Id.Should().Be(1);

// also check the 'http' call was like we expected it
var expectedUri = new Uri("http://test.com/api/test/whatever");

handlerMock.Protected().Verify(
   "SendAsync",
   Times.Exactly(1), // we expected a single external request
   ItExpr.Is<HttpRequestMessage>(req =>
      req.Method == HttpMethod.Get  // we expected a GET request
      && req.RequestUri == expectedUri // to this uri
   ),
   ItExpr.IsAny<CancellationToken>()
);

来源:https://gingter.org/2018/07/26/how-to-mock-httpclient-in-your-net-c-unit-tests/

我的一个同事注意到，大多数HttpClient方法都在底层调用SendAsync(HttpRequestMessage request, CancellationToken CancellationToken)，这是HttpMessageInvoker的一个虚拟方法:

所以到目前为止，模拟HttpClient最简单的方法就是简单地模拟这个特定的方法:

var mockClient = new Mock<HttpClient>();
mockClient.Setup(client => client.SendAsync(It.IsAny<HttpRequestMessage>(), It.IsAny<CancellationToken>())).ReturnsAsync(_mockResponse.Object);

并且您的代码可以调用大多数(但不是全部)HttpClient类方法，包括常规方法

httpClient.SendAsync(req)

点击这里确认 https://github.com/dotnet/corefx/blob/master/src/System.Net.Http/src/System/Net/Http/HttpClient.cs