如何使用作为参数传递的 CancellationToken 来模拟方法？

Question

我最近正在学习和使用 Polly 来为我的代码添加弹性，特别是对于超时和重试策略。 但是，我不知道如何使用 polly 对代码进行单元测试。 更具体地说，我不知道如何模拟以 Cancellation Token 作为参数的方法。 下面是我的代码结构

public class Caller
{
     private IHttpManager httpManager;
     private IAsyncPolicy<HttpResponseMessage> policyWrap;

     public Caller(IHttpManager httpManager, IAsyncPolicy<HttpResponseMessage> policyWrap)
     {
        this.httpManager= httpManager;
        this.policyWrap = policyWrap;
     }


     public async Task CallThirdParty()
     {      

        HttpResponseMessage httpResponse = await policyWrap.ExecuteAsync(async ct => await httpManager.TryCallThirdParty(ct), CancellationToken.None);

     }

}

public interface IHttpManager
{
    Task<HttpResponseMessage> TryCallThirdParty(CancellationToken cancellationToken);
}

---

下面是我打算运行但不知道如何运行的单元测试。

[Test]
public void TestBehaviourUnderTimeoutPolicy()
{
     // Set up the timeout policy such that the governed delegate will terminate after 1 sec if no response returned
     AsyncTimeoutPolicy<HttpResponseMessage> timeoutPolicy = Policy.TimeoutAsync<HttpResponseMessage>(1, TimeoutStrategy.Optimistic);


     // mock IHttpManager
     var mockHttpManager= new Mock<IHttpManager>();

     // THIS IS WHERE I'M HAVING TROUBLE WITH.
     // I want to simulate the behaviour of the method such that
     // it will throw an exception whenever the CancellationToken passed from the polly caller expires
     // But how can I do that with mock?
     mockHttpManager.Setup(m => m.TryCallThirdParty(It.IsAny<CancellationToken>()))).Returns(Task.Run(() => { Thread.Sleep(10000); return new HttpResponseMessage(); }));

     Caller c = new Caller(mockHttpManager.Object, timeoutPolicy);
     await c.CallThirdParty();

}

Answer 1

@Noremac 是对的（您在一个单元测试中测试了 2 个元素）。

但是，要回答“ CancellationToken时如何使Mock<T>抛出异常”的问题：使用Returns<TParam1, ...>(Func<TResult, TParam1>)重载。 为了清楚起见，我用CancellationTokenSource替换了AsyncTimeoutPolicy 。

// This test will perma-hang if the exception is not thrown
[TestMethod]
[ExpectedException(typeof(OperationCanceledException))]
public async Task TestMethod1()
{
    var source = new Mock<IHttpManager>();
    source.Setup(s => s.TryCallThirdParty(It.IsAny<CancellationToken>())).Returns<CancellationToken>(
        async token =>
        {
            // Wait until the token is cancelled
            await Task.Delay(Timeout.Infinite, token);
        });

    var tcs = new CancellationTokenSource(1000);
    await new Caller().Get(source.Object, tcs.Token);
}

Answer 2

您剪下的代码永远不会调用此方法“c.TryCallThirdParty”。

您是否尝试使用Task.Delay(Timespan.FromSeconds(1))而不是Thread.Sleep ？ 每次都使用 Task.Delay 而不是 Thread.Sleep 更好。