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?
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)。
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();
}
}
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
