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?
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/
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
这是一个老问题,但我有一种冲动,想用一个我在这里没有看到的解决方案来扩展答案。
您可以伪造Microsoft程序集(System.Net.Http),然后在测试期间使用ShinsContext。
In VS 2017, right click on the System.Net.Http assembly and choose "Add Fakes Assembly"
Put your code in the unit test method under a ShimsContext.Create() using. This way, you can isolate the code where you are planning to fake the HttpClient.
Depends on your implementation and test, I would suggest to implement all the desired acting where you call a method on the HttpClient and want to fake the returned value. Using ShimHttpClient.AllInstances will fake your implementation in all the instances created during your test. For example, if you want to fake the GetAsync() method, do the following:
[TestMethod]
public void FakeHttpClient()
{
using (ShimsContext.Create())
{
System.Net.Http.Fakes.ShimHttpClient.AllInstances.GetAsyncString = (c, requestUri) =>
{
//Return a service unavailable response
var httpResponseMessage = new HttpResponseMessage(HttpStatusCode.ServiceUnavailable);
var task = Task.FromResult(httpResponseMessage);
return task;
};
//your implementation will use the fake method(s) automatically
var client = new Connection(_httpClient);
client.doSomething();
}
}
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);