如何对委托处理程序进行单元测试

我有一个具有超时，重试，授权委托处理程序的httpClient。

        var authorizationHandler = new AuthorizationDelegatingHandler();
        var retryHandler = new RetryPolicyDelegatingHandler(3);
        var timeoutHandler = new TimeOutDelegatingHandler(TimeSpan.FromSeconds(5));
        

        authorizationHandler.InnerHandler = retryHandler;
        retryHandler.InnerHandler = timeoutHandler;

        _myHttpClient = new HttpClient(authorizationHandler);

我正在按照教程进行操作，并且尝试对超时处理程序进行单元测试

    [TestMethod]
    [ExpectedException(typeof(TimeoutException))]
    public async Task GetDocuments_Timeout_MustThrowTimeoutException()
    {

        var unauthorizedResponseHttpMessageHandlerMock = new Mock<HttpMessageHandler>();
        unauthorizedResponseHttpMessageHandlerMock.Protected().Setup<Task<HttpResponseMessage>>("SendAsync", ItExpr.IsAny<HttpRequestMessage>(), ItExpr.IsAny<CancellationToken>()).ReturnsAsync(new HttpResponseMessage()
        {
            StatusCode = System.Net.HttpStatusCode.Unauthorized
        });


        

        var httpClient = new HttpClient(unauthorizedResponseHttpMessageHandlerMock.Object);
        httpClient.BaseAddress = new Uri("http://localhost");
        var timeoutHandler = new TimeOutDelegatingHandler(TimeSpan.FromSeconds(3));
        var testableClass = new MyCustomclass(httpClient);
        var cancellationSource = new CancellationTokenSource();

        await testableClass.Foo();
    }

我被困在这一点上。如何在单元测试项目中链接这些处理程序？