我有一些问题,试图包装我的代码在单元测试中使用。问题在于。我有接口IHttpHandler:

public interface IHttpHandler
{
    HttpClient client { get; }
}

使用它的类HttpHandler:

public class HttpHandler : IHttpHandler
{
    public HttpClient client
    {
        get
        {
            return new HttpClient();
        }
    }
}

然后是Connection类,它使用simpleIOC注入客户端实现:

public class Connection
{
    private IHttpHandler _httpClient;

    public Connection(IHttpHandler httpClient)
    {
        _httpClient = httpClient;
    }
}

然后我有一个单元测试项目,它有这个类:

private IHttpHandler _httpClient;

[TestMethod]
public void TestMockConnection()
{
    var client = new Connection(_httpClient);
     
    client.doSomething();  

    // Here I want to somehow create a mock instance of the http client
    // Instead of the real one. How Should I approach this?     

}

现在很明显,我将在Connection类中拥有从后端检索数据(JSON)的方法。但是,我想为这个类编写单元测试,显然我不想针对真正的后端编写测试,而是一个模拟的后端。我试着给这个问题一个好的答案,但没有成功。我以前可以用Moq来模拟,但从来没有在HttpClient这样的东西上使用过。我应该如何处理这个问题?


当前回答

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

其他回答

一种替代方法是设置一个存根HTTP服务器,它根据与请求url匹配的模式返回罐装响应,这意味着您要测试真正的HTTP请求,而不是模拟。从历史上看,这将花费大量的开发工作,并将远远慢到考虑进行单元测试,然而,OSS库WireMock.net易于使用,足够快,可以运行大量的测试,所以可能值得考虑。Setup是几行代码:

var server = FluentMockServer.Start();
server.Given(
      Request.Create()
      .WithPath("/some/thing").UsingGet()
   )
   .RespondWith(
       Response.Create()
       .WithStatusCode(200)
       .WithHeader("Content-Type", "application/json")
       .WithBody("{'attr':'value'}")
   );

您可以在这里找到在测试中使用wiremock的更多细节和指导。

也许在您当前的项目中会有一些代码需要更改,但对于新项目,您绝对应该考虑使用Flurl。

https://flurl.dev

它是一个。net的HTTP客户端库,具有一个流畅的接口,特别支持使用它来发出HTTP请求的代码的可测试性。

网站上有很多代码示例,但简单地说,你在代码中是这样使用的。

添加用途。

using Flurl;
using Flurl.Http;

发送get请求并读取响应。

public async Task SendGetRequest()
{
   var response = await "https://example.com".GetAsync();
   // ...
}

在单元测试中,Flurl充当一个模拟,可以将其配置为所需的行为,还可以验证所执行的调用。

using (var httpTest = new HttpTest())
{
   // Arrange
   httpTest.RespondWith("OK", 200);

   // Act
   await sut.SendGetRequest();

   // Assert
   httpTest.ShouldHaveCalled("https://example.com")
      .WithVerb(HttpMethod.Get);
}

因为HttpClient使用SendAsync方法来执行所有的HTTP请求,你可以重写SendAsync方法并模拟HttpClient。

对于将HttpClient创建到接口的封装,如下所示

public interface IServiceHelper
{
    HttpClient GetClient();
}

然后在您的服务中使用上述接口进行依赖注入,示例如下

public class SampleService
{
    private readonly IServiceHelper serviceHelper;

    public SampleService(IServiceHelper serviceHelper)
    {
        this.serviceHelper = serviceHelper;
    }

    public async Task<HttpResponseMessage> Get(int dummyParam)
    {
        try
        {
            var dummyUrl = "http://www.dummyurl.com/api/controller/" + dummyParam;
            var client = serviceHelper.GetClient();
            HttpResponseMessage response = await client.GetAsync(dummyUrl);               

            return response;
        }
        catch (Exception)
        {
            // log.
            throw;
        }
    }
}

Now in unit test project create a helper class for mocking SendAsync. Here it is a FakeHttpResponseHandler class which is inheriting DelegatingHandler which will provide an option to override the SendAsync method. After overriding the SendAsync method need to setup a response for each HTTP Request which is calling SendAsync method, for that create a Dictionary with key as Uri and value as HttpResponseMessage so that whenever there is a HTTP Request and if the Uri matches SendAsync will return the configured HttpResponseMessage.

public class FakeHttpResponseHandler : DelegatingHandler
{
    private readonly IDictionary<Uri, HttpResponseMessage> fakeServiceResponse;
    private readonly JavaScriptSerializer javaScriptSerializer;
    public FakeHttpResponseHandler()
    {
        fakeServiceResponse =  new Dictionary<Uri, HttpResponseMessage>();
        javaScriptSerializer =  new JavaScriptSerializer();
    }

    /// <summary>
    /// Used for adding fake httpResponseMessage for the httpClient operation.
    /// </summary>
    /// <typeparam name="TQueryStringParameter"> query string parameter </typeparam>
    /// <param name="uri">Service end point URL.</param>
    /// <param name="httpResponseMessage"> Response expected when the service called.</param>
    public void AddFakeServiceResponse(Uri uri, HttpResponseMessage httpResponseMessage)
    {
        fakeServiceResponse.Remove(uri);
        fakeServiceResponse.Add(uri, httpResponseMessage);
    }

    /// <summary>
    /// Used for adding fake httpResponseMessage for the httpClient operation having query string parameter.
    /// </summary>
    /// <typeparam name="TQueryStringParameter"> query string parameter </typeparam>
    /// <param name="uri">Service end point URL.</param>
    /// <param name="httpResponseMessage"> Response expected when the service called.</param>
    /// <param name="requestParameter">Query string parameter.</param>
    public void AddFakeServiceResponse<TQueryStringParameter>(Uri uri, HttpResponseMessage httpResponseMessage, TQueryStringParameter requestParameter)
    {
        var serilizedQueryStringParameter = javaScriptSerializer.Serialize(requestParameter);
        var actualUri = new Uri(string.Concat(uri, serilizedQueryStringParameter));
        fakeServiceResponse.Remove(actualUri);
        fakeServiceResponse.Add(actualUri, httpResponseMessage);
    }

    // all method in HttpClient call use SendAsync method internally so we are overriding that method here.
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        if(fakeServiceResponse.ContainsKey(request.RequestUri))
        {
            return Task.FromResult(fakeServiceResponse[request.RequestUri]);
        }

        return Task.FromResult(new HttpResponseMessage(HttpStatusCode.NotFound)
        {
            RequestMessage = request,
            Content = new StringContent("Not matching fake found")
        });
    }
}

通过模仿框架或如下所示创建IServiceHelper的新实现。 我们可以使用这个FakeServiceHelper类来注入FakeHttpResponseHandler类,这样每当这个类创建HttpClient时,它都会使用FakeHttpResponseHandler类而不是实际的实现。

public class FakeServiceHelper : IServiceHelper
{
    private readonly DelegatingHandler delegatingHandler;

    public FakeServiceHelper(DelegatingHandler delegatingHandler)
    {
        this.delegatingHandler = delegatingHandler;
    }

    public HttpClient GetClient()
    {
        return new HttpClient(delegatingHandler);
    }
}

And in test configure FakeHttpResponseHandler class by adding the Uri and expected HttpResponseMessage. The Uri should be the actual serviceendpoint Uri so that when the overridden SendAsync method is called from actual service implementation it will match the Uri in Dictionary and respond with the configured HttpResponseMessage. After configuring inject the FakeHttpResponseHandler object to the fake IServiceHelper implementation. Then inject the FakeServiceHelper class to the actual service which will make the actual service to use the override SendAsync method.

[TestClass]
public class SampleServiceTest
{
    private FakeHttpResponseHandler fakeHttpResponseHandler;

    [TestInitialize]
    public void Initialize()
    {
        fakeHttpResponseHandler = new FakeHttpResponseHandler();
    }

    [TestMethod]
    public async Task GetMethodShouldReturnFakeResponse()
    {
        Uri uri = new Uri("http://www.dummyurl.com/api/controller/");
        const int dummyParam = 123456;
        const string expectdBody = "Expected Response";

        var expectedHttpResponseMessage = new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new StringContent(expectdBody)
        };

        fakeHttpResponseHandler.AddFakeServiceResponse(uri, expectedHttpResponseMessage, dummyParam);

        var fakeServiceHelper = new FakeServiceHelper(fakeHttpResponseHandler);

        var sut = new SampleService(fakeServiceHelper);

        var response = await sut.Get(dummyParam);

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

        Assert.AreEqual(HttpStatusCode.OK, response.StatusCode);
        Assert.AreEqual(expectdBody, responseBody);
    }
}

GitHub链接:有示例实现

不要有一个包装器来创建一个新的HttpClient实例。如果您这样做,您将在运行时耗尽套接字(即使您正在处理HttpClient对象)。

如果使用MOQ,正确的做法是添加使用MOQ . protected;到您的测试,然后编写如下代码:

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


var httpClient = new HttpClient(mockHttpMessageHandler.Object);

这是一个常见的问题,我非常希望能够模拟HttpClient,但我想我最终意识到不应该模拟HttpClient。这样做似乎是合乎逻辑的,但我认为我们已经被我们在开源库中看到的东西洗脑了。

We often see "Clients" out there that we mock in our code so that we can test in isolation, so we automatically try to apply the same principle to HttpClient. HttpClient actually does a lot; you can think of it as a manager for HttpMessageHandler, so you don't wanna mock that, and that's why it still doesn't have an interface. The part that you're really interested in for unit testing, or designing your services, even, is the HttpMessageHandler since that is what returns the response, and you can mock that.

同样值得指出的是,您可能应该开始把HttpClient当作一个更大的交易来对待。例如:让你的新HttpClients的实例化最小化。重复使用它们,它们被设计成可重复使用的,如果你这样做,会使用更少的资源。如果您开始把它当作一个更大的事情来对待,那么想要模拟它就会感觉更错误,现在消息处理程序将开始成为您正在注入的东西,而不是客户端。

换句话说,围绕处理程序而不是客户端设计依赖项。更好的是,使用HttpClient的抽象“服务”允许你注入一个处理程序,并将其作为你的可注入依赖项。事实上,HttpClientFactor(您应该使用它)被设计为带有注入消息处理程序的扩展。然后在测试中,可以伪造处理程序来控制设置测试的响应。

包装HttpClient是一种疯狂的时间浪费。

更新: 请看约书亚·杜姆斯的例子。这正是我所推荐的。