使用 Moq 模拟 HttpClient

Question

我想对使用HttpClient 的类进行单元测试。我们在类构造函数中注入了HttpClient 对象。

public class ClassA : IClassA
{
    private readonly HttpClient _httpClient;

    public ClassA(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }

    public async Task<HttpResponseMessage> SendRequest(SomeObject someObject)
    {
        //Do some stuff

        var request = new HttpRequestMessage(HttpMethod.Post, "http://some-domain.in");

        //Build the request

        var response = await _httpClient.SendAsync(request);

        return response;
    }
}

现在我们要对ClassA.SendRequest 方法进行单元测试。我们将Ms Test 用于单元测试框架，Moq 用于模拟。

当我们尝试模拟 HttpClient 时，它会抛出 NotSupportedException。

[TestMethod]
public async Task SendRequestAsync_Test()
{
    var mockHttpClient = new Mock<HttpClient>();

    mockHttpClient.Setup(
        m => m.SendAsync(It.IsAny<HttpRequestMessage>()))
    .Returns(() => Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)));
}

我们如何解决这个问题？

Answer 1

那个特定的重载方法不是虚拟的，所以不能被 Moq 覆盖。

public Task<HttpResponseMessage> SendAsync(HttpRequestMessage request);

这就是为什么它抛出NotSupportedException

你要找的虚方法就是这个方法

public virtual Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken);

然而，模拟 HttpClient 并不像其内部消息处理程序看起来那么简单。

我建议使用带有自定义消息处理程序存根的具体客户端，这将在伪造请求时提供更大的灵活性。

这是一个委托处理程序存根的示例。

public class DelegatingHandlerStub : DelegatingHandler {
    private readonly Func<HttpRequestMessage, CancellationToken, Task<HttpResponseMessage>> _handlerFunc;
    public DelegatingHandlerStub() {
        _handlerFunc = (request, cancellationToken) => Task.FromResult(request.CreateResponse(HttpStatusCode.OK));
    }

    public DelegatingHandlerStub(Func<HttpRequestMessage, CancellationToken, Task<HttpResponseMessage>> handlerFunc) {
        _handlerFunc = handlerFunc;
    }

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

请注意，默认构造函数基本上是在做你之前试图模拟的事情。它还允许为请求提供更多自定义场景。

使用存根，可以将测试重构为类似

public async Task _SendRequestAsync_Test() {
    //Arrange           
    var handlerStub = new DelegatingHandlerStub();
    var client = new HttpClient(handlerStub);
    var sut = new ClassA(client);
    var obj = new SomeObject() {
        //Populate
    };

    //Act
    var response = await sut.SendRequest(obj);

    //Assert
    Assert.IsNotNull(response);
    Assert.IsTrue(response.IsSuccessStatusCode);
}

Answer 2

Moq 可以模拟出受保护的方法，例如 HttpMessageHandler 上的 SendAsync，您可以在其构造函数中提供给 HttpClient。

var mockHttpMessageHandler = new Mock<HttpMessageHandler>();
mockHttpMessageHandler.Protected()
    .Setup<Task<HttpResponseMessage>>("SendAsync", ItExpr.IsAny<HttpRequestMessage>(), ItExpr.IsAny<CancellationToken>())
    .ReturnsAsync(new HttpResponseMessage
    {
        StatusCode = HttpStatusCode.OK
     });

var client = new HttpClient(mockHttpMessageHandler.Object);

复制自https://thecodebuzz.com/unit-test-mock-httpclientfactory-moq-net-core/

Answer 3

使用 HttpClient 进行适当的模拟是一项艰巨的工作，因为它是在大多数人在 dotnet 中进行单元测试之前编写的。有时我会设置一个存根 HTTP 服务器，它根据与请求 url 匹配的模式返回预设响应，这意味着您测试真正的 HTTP 请求不是模拟，而是到 localhost 服务器。使用WireMock.net 使这变得非常简单，并且运行速度足够快，可以满足我的大部分单元测试需求。

所以不要使用http://some-domain.in，而是在某个端口上使用本地主机服务器设置，然后：

var server = FluentMockServer.Start(/*server and port can be setup here*/);
server.Given(
      Request.Create()
      .WithPath("/").UsingPost()
   )
   .RespondWith(
       Response.Create()
       .WithStatusCode(200)
       .WithHeader("Content-Type", "application/json")
       .WithBody("{'attr':'value'}")
   );

您可以找到更多详细信息和guidance on using wiremock in tests here.

Answer 4

我最近不得不模拟 HttpClient，我使用了Moq.Contrib.HttpClient。这是我需要的，而且使用简单，所以我想我会把它扔掉。

以下是一般用法示例：

// All requests made with HttpClient go through its handler's SendAsync() which we mock
var handler = new Mock<HttpMessageHandler>();
var client = handler.CreateClient();

// A simple example that returns 404 for any request
handler.SetupAnyRequest()
    .ReturnsResponse(HttpStatusCode.NotFound);

// Match GET requests to an endpoint that returns json (defaults to 200 OK)
handler.SetupRequest(HttpMethod.Get, "https://example.com/api/stuff")
    .ReturnsResponse(JsonConvert.SerializeObject(model), "application/json");

// Setting additional headers on the response using the optional configure action
handler.SetupRequest("https://example.com/api/stuff")
    .ReturnsResponse(bytes, configure: response =>
    {
        response.Content.Headers.LastModified = new DateTime(2018, 3, 9);
    })
    .Verifiable(); // Naturally we can use Moq methods as well

// Verify methods are provided matching the setup helpers
handler.VerifyAnyRequest(Times.Exactly(3));

更多信息，请查看作者的博文here。