如何测试是否在ASP.NET Core中调用UseDeveloperExceptionPage中间件？

如何解决如何测试是否在ASP.NET Core中调用UseDeveloperExceptionPage中间件？

我的情况确实很棘手。我需要测试抛出异常时是否正在调用UseDeveloperExceptionPage中间件。 为了实现这一目标，我编写了一些辅助代码。

DiagnosticExceptionAssembly.cs

namespace TestProjectSample
{
    internal static class DiagnosticExceptionAssembly
    {
        internal const string Assembly = "Microsoft.AspNetCore.Diagnostics.UnhandledException";
    }
}

ExceptionMessage.cs

namespace TestProjectSample
{
    public struct ExceptionMessage
    {
        public string Message { get; set; }
    }
}

ExceptionMessageObserver.cs

using System;

namespace TestProjectSample
{
    public class ExceptionMessageObserver : IExceptionMessage
    {
        public string Message { get; set; }

        public void OnCompleted()
        {
            throw new NotImplementedException();
        }

        public void OnError(Exception error)
        {
            throw new NotImplementedException();
        }

        public void OnNext(ExceptionMessage value)
        {
            Message = value.Message;
        }
    }

    public interface IExceptionMessage : IObserver<ExceptionMessage>
    {
        string Message { get; set; }
    }
}

ExceptionObserver.cs

using System;
using System.Collections.Generic;
using System.Reflection;

namespace TestProjectSample
{
    public class ExceptionObserver : IObserver<KeyValuePair<string,object>>
    {
        private readonly IObserver<ExceptionMessage> _exceptionMessage;

        public ExceptionObserver(IObserver<ExceptionMessage> exceptionMessage)
        {
            _exceptionMessage = exceptionMessage;
        }

        public void OnCompleted()
        {
            throw new NotImplementedException();
        }

        public void OnError(Exception error)
        {
            throw new NotImplementedException();
        }

        public void OnNext(KeyValuePair<string,object> value)
        {
            switch (value.Key)
            {
                case DiagnosticExceptionAssembly.Assembly:
                    var exceptionPayload = value.Value
                        .GetType()
                        .GetTypeInfo()
                        .GetDeclaredProperty("Exception")?
                        .GetValue(value.Value) as string;
                    _exceptionMessage.OnNext(new ExceptionMessage {Message = exceptionPayload});
                    break;
            }
        }
    }
}

ExceptionSubscriber.cs

using System;
using System.Diagnostics;

namespace TestProjectSample
{
    public class ExceptionSubscriber : IObserver<DiagnosticListener>
    {
        private readonly IObserver<ExceptionMessage> _exceptionMessage;

        public ExceptionSubscriber(IObserver<ExceptionMessage> exceptionMessage)
        {
            _exceptionMessage = exceptionMessage;
        }
        
        public void OnCompleted()
        {
            throw new NotImplementedException();
        }

        public void OnError(Exception error)
        {
            throw new NotImplementedException();
        }

        public void OnNext(DiagnosticListener value)
        {
            if (string.Equals(DiagnosticExceptionAssembly.Assembly,value.Name))
            {
                value.Subscribe(new ExceptionObserver(_exceptionMessage));
            }
        }
    }
}

DevExceptionPageFacts.cs

using System.Diagnostics;
using System.Net;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.TestHost;
using Microsoft.Extensions.Hosting;
using Xunit;

namespace TestProjectSample
{
    public class DevExceptionPageFacts
    {
        private readonly IHostBuilder _hostBuilder;

        private static readonly IExceptionMessage ExceptionMessage = new ExceptionMessageObserver();

        public DevExceptionPageFacts()
        {
            FactSubscriber();
            _hostBuilder = GenerateExceptionHostBuilder();
        }

        private static IHostBuilder GenerateExceptionHostBuilder()
        {
            return new HostBuilder()
                .ConfigureWebHost(builder =>
                {
                    builder.UseTestServer();
                    builder.Configure(applicationBuilder =>
                    {
                        applicationBuilder.UseDeveloperExceptionPage();
                        applicationBuilder.Run(context => throw new HttpResetTestException(1));
                    });
                });
        }

        private static void FactSubscriber()
        {
            DiagnosticListener.AllListeners.Subscribe(new ExceptionSubscriber(ExceptionMessage));
        }

        [Fact]
        public async Task Throw_DevelopmentPageException()
        {
            var host = await _hostBuilder.StartAsync();
            using var client = host.GetTestClient();
            var response = await client.GetAsync("/");
            Assert.Equal(HttpStatusCode.InternalServerError,response.StatusCode);
            Assert.NotNull(ExceptionMessage.Message);
        }
    }
}

研究UseDeveloperExceptionPage的源代码我已经注意到DiagnosticSource的注入，因此我决定创建一个类来侦听中间件引发和捕获异常时的情况。但是我的测试没有通过。有人知道如何通过此测试吗？