无法在单元测试中模拟 HttpClient PostAsync()

Question

我正在使用 xUnit 和 Moq 编写测试用例。

我正在尝试模拟 HttpClient 的 PostAsync()，但出现错误。

下面是用于模拟的代码：

   public TestADLS_Operations()
    {
        var mockClient = new Mock<HttpClient>();
        mockClient.Setup(repo => repo.PostAsync(It.IsAny<string>(), It.IsAny<HttpContent>())).Returns(() => Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)));

        this._iADLS_Operations = new ADLS_Operations(mockClient.Object);
    }

错误：

不支持的表达式：repo => repo.PostAsync(It.IsAny(), It.IsAny()) 不可覆盖的成员（这里： HttpClient.PostAsync) 不能用于设置/验证 表达式。

截图：

Answer 1

不要在代码中直接使用 HttpClient 实例，而是使用 IHttpClientFactory。 然后，在您的测试中，您可以创建自己的 IHttpClientFactory 实现，该实现发送回连接到 TestServer 的 HttpClient。

以下是您的假工厂的示例：

public class InMemoryHttpClientFactory: IHttpClientFactory
{
    private readonly TestServer _server;

    public InMemoryHttpClientFactory(TestServer server)
    {
        _server = server;
    }

    public HttpClient CreateClient(string name)
    {
        return _server.CreateClient();
    }
}

然后您可以在您的测试中设置一个 TestServer 并让您的自定义 IHttpClientFactory 为该服务器创建客户端：

public TestADLS_Operations()
{
    //setup TestServer
    IWebHostBuilder hostBuilder = new WebHostBuilder()
        .Configure(app => app.Run(
        async context =>
    {
        // set your response headers via the context.Response.Headers property
        // set your response content like this:
        byte[] content = Encoding.Unicode.GetBytes("myResponseContent");
        await context.Response.Body.WriteAsync(content);
    }));
    var testServer = new TestServer(hostBuilder)

    var factory = new InMemoryHttpClientFactory(testServer);
    _iADLS_Operations = new ADLS_Operations(factory);

    [...]
}

Answer 2

您遇到的问题表明耦合紧密，您可以通过引入中间抽象来解决它。您可能希望创建一个类来聚合 HttpClient 并通过接口公开 PostAsync() 方法：

// Now you mock this interface instead, which is a pretty simple task.
// I suggest also abstracting away from an HttpResponseMessage
// This would allow you to swap for any other transport in the future. All 
// of the response error handling could be done inside the message transport 
// class.  
public interface IMessageTransport
{
    Task SendMessageAsync(string message);
}

// In ADLS_Operations ctor:
public ADLS_Operations(IMessageTransport messageTransport)
{ 
    //...
}

public class HttpMessageTransport : IMessageTransport
{
    public HttpMessageTransport()
    {
        this.httpClient = //get the http client somewhere.
    }

    public Task SendMessageAsync(string message)
    {
        return this.httpClient.PostAsync(message);
    }
}

Answer 3

不可覆盖的成员（此处为：HttpClient.PostAsync）不得用于设置/验证表达式。

我也尝试像你一样模拟HttpClient，我得到了同样的错误信息。

解决方案：

不要模拟HttpClient，而是模拟HttpMessageHandler。

然后将mockHttpMessageHandler.Object 提供给您的HttpClient，然后将其传递给您的产品代码类。这是因为HttpClient 在后台使用HttpMessageHandler：

// Arrange
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);
this._iADLS_Operations = new ADLS_Operations(client);

注意：您还需要一个

using Moq.Protected;

在测试文件的顶部。

然后您可以从您的测试中调用使用PostAsync 的方法，PostAsync 将返回 HTTP 状态 OK 响应：

// Act
var returnedItem = this._iADLS_Operations.MethodThatUsesPostAsync(/*parameter(s) here*/);

优势： 模拟HttpMessageHandler 意味着您的产品代码或测试代码中不需要额外的类。

有用的资源：

1. Unit Testing with the HttpClient
2. How to mock HttpClient in your .NET / C# unit tests

Answer 4

正如其他答案所解释的，您应该模拟 HttpMessageHandler 或 HttpClientFactory，而不是 HttpClient。这是一种常见的情况，有人为 both 案例创建了一个帮助程序库，Moq.Contrib.HttpClient。

从 HttpClient 的 General Usage 示例复制：

// 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));

对于 HttpClientFactory ：

var handler = new Mock<HttpMessageHandler>();
var factory = handler.CreateClientFactory();

// Named clients can be configured as well (overriding the default)
Mock.Get(factory).Setup(x => x.CreateClient("api"))
    .Returns(() =>
    {
        var client = handler.CreateClient();
        client.BaseAddress = ApiBaseUrl;
        return client;
    });

Answer 5

Visit Blog

内置支持在 HttpRequestMessage 的 HttpMethod 和 RequestUri 属性上应用条件。这样我们就可以使用 EndsWith 方法模拟各种路径的 HttpGet、HttpPost 和其他动词，如下所述。

_httpMessageHandler.Protected()
      .Setup<Task<HttpResponseMessage>>("SendAsync", true,          
      *// Specify conditions for httpMethod and path
      ItExpr.Is<HttpRequestMessage>(req => req.Method == HttpMethod.Get
           && req.RequestUri.AbsolutePath.EndsWith($"{path}"))),*
      ItExpr.IsAny<CancellationToken>())
      .ReturnsAsync(new HttpResponseMessage
      {
           StatusCode = HttpStatusCode.OK,
           Content = new StringContent("_0Kvpzc")
       });