FakeItEasy

Question

我运行难以使用 FakeItEasy 测试 System.Net.Http.HttpClient。考虑这种情况：

//Service that consumes HttpClient
public class LoggingService
{
    private readonly HttpClient _client;

    public LoggingService(HttpClient client)
    {
        _client = client;
        _client.BaseAddress = new Uri("http://www.example.com");
    }

    public async Task Log(LogEntry logEntry)
    {
        var json = JsonConvert.SerializeObject(logEntry);
        var httpContent = new StringContent(json, Encoding.UTF8, "application/json");
        await _client.PostAsync("/api/logging", httpContent);
    }
}

public class LogEntry
{
    public string MessageText { get; set; }
    public DateTime DateLogged { get; set; }
}

单元测试

从单元测试的角度来看，我想验证 HttpClient 是否将指定的 logEntry 负载发布到适当的 URL (http://www.example.com/api/logging)。（旁注：我无法直接测试 HttpClient.PostAsync() 方法，因为我的服务使用 HttpClient 的具体实现，而 Microsoft 没有为其提供接口。但是，我可以创建自己的HttpClient 使用 FakeMessageHandler（下方）作为依赖项，并将其注入服务以进行测试。从那里，我可以测试 DoSendAsync()

//Helper class for mocking the MessageHandler dependency of HttpClient
public abstract class FakeMessageHandler : HttpMessageHandler
{
    protected sealed override Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request,
        CancellationToken cancellationToken)
    {
        return DoSendAsync(request);
    }

    public abstract Task<HttpResponseMessage> DoSendAsync(HttpRequestMessage request);
}

理论上，我应该可以使用FakeItEasy中的Matches()方法来编写自定义匹配函数。这看起来像这样：

//NUnit Test
[TestFixture]
public class LoggingServiceTests
{
    private LoggingService _loggingService;
    private FakeMessageHandler _fakeMessageHandler;
    private HttpClient _httpClient;

    [SetUp]
    public void SetUp()
    {
        _fakeMessageHandler = A.Fake<FakeMessageHandler>();
        _httpClient = new HttpClient(_fakeMessageHandler);
        _loggingService = new LoggingService(_httpClient);
    }

    [Test]
    public async Task Logs_Error_Successfully()
    {
        var dateTime = new DateTime(2016, 11, 3);
        var logEntry = new LogEntry
        {
            MessageText = "Fake Message",
            DateLogged = dateTime
        };
        await _loggingService.Log(logEntry);

        A.CallTo(() => _fakeMessageHandler.DoSendAsync(
            A<HttpRequestMessage>.That.Matches(
                m => DoesLogEntryMatch("Fake Message", dateTime, HttpMethod.Post,
                    "https://www.example.com/api/logging", m)))
        ).MustHaveHappenedOnceExactly();
    }


    private bool DoesLogEntryMatch(string expectedMessageText, DateTime expectedDateLogged,
        HttpMethod expectedMethod, string expectedUrl, HttpRequestMessage actualMessage)
    {
        //TODO: still need to check expectedMessageText and expectedDateLogged from the HttpRequestMessage content
        return actualMessage.Method == expectedMethod && actualMessage.RequestUri.ToString() == expectedUrl;
    }


}

检查 URL 和 HttpMethod 非常简单（如上所示）。但是，为了检查负载，我需要检查 HttpRequestMessage 的内容。这就是它变得棘手的地方。我发现读取 HttpRequestMessage 内容的唯一方法是使用一种内置的异步方法（即 ReadAsStringAsync、ReadAsByteArrayAsync、ReadAsStreamAsync 等）据我所知，FakeItEasy 不支持 async/await Matches() 谓词内部的操作。这是我尝试过的：

将 DoesLogEntryMatch() 方法转换为异步，并等待 ReadAsStringAsync() 调用 （不起作用）

    //Compiler error - Cannot convert async lambda expression to delegate type 'Func<HttpRequestMessage, bool>'.
    //An async lambda expression may return void, Task or Task<T>,
    //none of which are convertible to 'Func<HttpRequestMessage, bool>'
    A.CallTo(() => _fakeMessageHandler.DoSendAsync(
        A<HttpRequestMessage>.That.Matches(
            async m => await DoesLogEntryMatch("Fake Message", dateTime, HttpMethod.Post,
                "http://www.example.com/api/logging", m)))
    ).MustHaveHappenedOnceExactly();


private async Task<bool> DoesLogEntryMatch(string expectedMessageText, DateTime expectedDateLogged,
    HttpMethod expectedMethod, string expectedUrl, HttpRequestMessage actualMessage)
{
    var message = await actualMessage.Content.ReadAsStringAsync();
    var logEntry = JsonConvert.DeserializeObject<LogEntry>(message);

    return logEntry.MessageText == expectedMessageText &&
           logEntry.DateLogged == expectedDateLogged &&
    actualMessage.Method == expectedMethod && actualMessage.RequestUri.ToString() == expectedUrl;
}

将 DoesLogEntryMatch 保留为非异步方法，不要等待 ReadAsStringAsync()。这在我测试时似乎有效，但我了解到这样做在某些情况下可能会导致死锁。

private bool DoesLogEntryMatch(string expectedMessageText, DateTime expectedDateLogged,
    HttpMethod expectedMethod, string expectedUrl, HttpRequestMessage actualMessage)
{
    var message = actualMessage.Content.ReadAsStringAsync().Result;
    var logEntry = JsonConvert.DeserializeObject<LogEntry>(message);

    return logEntry.MessageText == expectedMessageText &&
           logEntry.DateLogged == expectedDateLogged &&
    actualMessage.Method == expectedMethod && actualMessage.RequestUri.ToString() == expectedUrl;
}

将 DoesLogEntryMatch 保留为非异步方法，并在 Task.Run() 内等待 ReadAsStringAsync()。这会生成一个等待结果的新线程，但允许同步调用运行的原始方法。据我所知，这是从同步上下文调用异步方法的唯一 "safe" 方法（即没有死锁）。这就是我最后要做的。

private bool DoesLogEntryMatch(string expectedMessageText, DateTime expectedDateLogged,
    HttpMethod expectedMethod, string expectedUrl, HttpRequestMessage actualMessage)
{
    var message = Task.Run(async () => await actualMessage.Content.ReadAsStringAsync()).Result;
    var logEntry = JsonConvert.DeserializeObject<LogEntry>(message);

    return logEntry.MessageText == expectedMessageText &&
           logEntry.DateLogged == expectedDateLogged &&
    actualMessage.Method == expectedMethod && actualMessage.RequestUri.ToString() == expectedUrl;
}

所以，我成功了，但似乎在 FakeItEasy 中应该有更好的方法来做到这一点。是否有等效于 MatchesAsync() 方法的方法，该方法采用支持 async/await 的谓词？

Answer 1

FakeItEasy 中没有MatchesAsync；也许它是可以添加的东西（当然它只能用于异步方法）。

Leave DoesLogEntryMatch as a non-async method, and don't await ReadAsStringAsync(). This seems to work when I tested it, but I have read that doing this could cause deadlocks in certain situations.

事实上，我认为这是正确的做法。强烈建议不要在应用程序代码中使用 .Wait() 或 .Result，但你不是在应用程序代码中，而是在单元测试中。可能发生的死锁是由SynchronizationContext的存在引起的，它存在于某些框架中（桌面框架如WPF或WinForms，经典ASP.NET），但不在单元测试的上下文中，所以你应该没事。我过去成功地使用了相同的方法。

FakeItEasy - 是否可以异步测试约束（即 MatchesAsync）？

FakeItEasy - Is it possible to test constraints asynchronously (i.e. MatchesAsync)?

c#

asynchronous

async-await

dotnet-httpclient