由于HttpClient使用SendAsyncmethod来执行所有操作HTTP Requests，因此您可以override SendAsync方法和模拟HttpClient。
对于该包装，创建HttpClient为interface，如下所示
public interface IServiceHelper
{
HttpClient GetClient();
}
然后interface在服务中使用上面的依赖注入，下面的示例
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;
}
}
}
现在在单元测试项目中，创建一个用于模拟的助手类SendAsync。这里是一个FakeHttpResponseHandler类，inheriting DelegatingHandler它将提供一个替代SendAsync方法的选项。重写后SendAsync的方法需要设定每个响应HTTP Request该调用SendAsync方法，为创造一个Dictionary有key作为Uri和value作为HttpResponseMessage等等，只要有一个HTTP Request，如果Uri比赛SendAsync将返回配置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")
});
}
}
IServiceHelper通过嘲笑框架或下面的类似方法创建一个新的实现。这FakeServiceHelper节课我们可以用它来注入FakeHttpResponseHandler类，以便每当HttpClient这个创造了class将使用FakeHttpResponseHandler class而不是实际的执行情况。
public class FakeServiceHelper : IServiceHelper
{
private readonly DelegatingHandler delegatingHandler;
public FakeServiceHelper(DelegatingHandler delegatingHandler)
{
this.delegatingHandler = delegatingHandler;
}
public HttpClient GetClient()
{
return new HttpClient(delegatingHandler);
}
}
并在测试中FakeHttpResponseHandler class通过添加Uri和预期进行配置HttpResponseMessage。本Uri应该是实际的service端点Uri，以便当overridden SendAsync方法是从实际称为service实施其将匹配Uri在Dictionary与配置的响应HttpResponseMessage。配置完成后，将注入FakeHttpResponseHandler object伪造的IServiceHelper实现。然后将注入FakeServiceHelper class到实际服务中，这将使实际服务使用该override SendAsync方法。
[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：具有示例实现
HttpClient在哪里？您正在强迫客户使用HttpClient具体的类。相反，你应该暴露一个抽象的HttpClient。