Spec fails when run by mspec.exe, but passes when

问题:

I wrote about this topic in another question.

However, I've since refactored my code to get rid of configuration access, thus allowing the specs to pass. Or so I thought. They run fine from within Visual Studio using TestDriven.Net. However, when I run them during rake using the mspec.exe tool, they still fail with a serialization exception. So I've created a completely self-contained example that does basically nothing except setup fake security credentials on the thread. This test passes just fine in TD.Net, but blows up in mspec.exe. Does anybody have any suggestions?

Update: I've discovered a work-around. After researching the issue, it seems the cause is that the assembly containing my principal object is not in the same folder as the mspec.exe. When mspec creates a new AppDomain to run my specs, that new AppDomain has to load the assembly with the principal object in order to deserialize it. That assembly is not in the same folder as the mspec EXE, so it fails. If I copied my assembly into the same folder as mspec, it works fine.

What I still don't understand is why ReSharper and TD.Net can run the test just fine? Do they not use mspec.exe to actually run the tests?

using System;
using System.Security.Principal;
using System.Threading;
using Machine.Specifications;

namespace MSpecTest
{
    [Subject(typeof(MyViewModel))]
    public class When_security_credentials_are_faked 
    {
        static MyViewModel SUT;

        Establish context = SetupFakeSecurityCredentials;

        Because of = () =>
            SUT = new MyViewModel();

        It should_be_initialized = () =>
            SUT.Initialized.ShouldBeTrue();

        static void SetupFakeSecurityCredentials()
        {
            Thread.CurrentPrincipal = CreatePrincipal(CreateIdentity());
        }

        static MyIdentity CreateIdentity()
        {
            return new MyIdentity(Environment.UserName, "None", true);
        }

        static MyPrincipal CreatePrincipal(MyIdentity identity)
        {
            return new MyPrincipal(identity);
        }
    }

    public class MyViewModel
    {
        public MyViewModel()
        {
            Initialized = true;
        }

        public bool Initialized { get; set; }
    }

    [Serializable]
    public class MyPrincipal : IPrincipal
    {
        private readonly MyIdentity _identity;

        public MyPrincipal(MyIdentity identity)
        {
            _identity = identity;
        }

        public bool IsInRole(string role)
        {
            return true;
        }

        public IIdentity Identity
        {
            get { return _identity; }
        }
    }

    [Serializable]
    public class MyIdentity : IIdentity
    {
        private readonly string _name;
        private readonly string _authenticationType;
        private readonly bool _isAuthenticated;

        public MyIdentity(string name, string authenticationType, bool isAuthenticated)
        {
            _name = name;
            _isAuthenticated = isAuthenticated;
            _authenticationType = authenticationType;
        }

        public string Name
        {
            get { return _name; }
        }

        public string AuthenticationType
        {
            get { return _authenticationType; }
        }

        public bool IsAuthenticated
        {
            get { return _isAuthenticated; }
        }
    }
}

回答1:

Dan,

thank you for providing a reproduction.

First off, the console runner works differently than the TestDriven.NET and ReSharper runners. Basically, the console runner has to perform a lot more setup work in that it creates a new AppDomain (plus configuration) for every assembly that is run. This is required to load the .dll.config file for your spec assembly.

Per spec assembly, two AppDomains are created:

1. The first AppDomain (Console) is created implicitly when mspec.exe is executed,
2. a second AppDomain is created by mspec.exe for the assembly containing the specs (Spec).

Both AppDomains communicate with each other through .NET Remoting: For example, when a spec is executed in the Spec AppDomain, it notifies the Console AppDomain of that fact. When Console receives the notification it acts accordingly by writing the spec information to the console.

This communiciation between Spec and Console is realized transparently through .NET Remoting. One property of .NET Remoting is that some properties of the calling AppDomain (Spec) are automatically included when sending notifications to the target AppDomain (Console). Thread.CurrentPrincipal is such a property. You can read more about that here: http://sontek.vox.com/library/post/re-iprincipal-iidentity-ihttpmodule-serializable.html

The context you provide will run in the Spec AppDomain. You set Thread.CurrentPrincipal in the Because. After Because ran, a notification will be issued to the Console AppDomain. The notification will include your custom MyPrincipal that the receiving Console AppDomain tries to deserialize. It cannot do that since it doesn't know about your spec assembly (as it is not included in its private bin path).

This is why you had to put your spec assembly in the same folder as mspec.exe.

There are two possible workarounds:

1. Derive MyPrincipal and MyIdentity from MarshalByRefObject so that they can take part in cross-AppDomain communication through a proxy (instead of being serialized)
2. Set Thread.CurrentPrincipal transiently in the Because

(Text is required for formatting to work -- please ignore)

Because of = () => 
{
    var previousPrincipal = Thread.CurrentPrincipal;
    try
    {
        Thread.CurrentPrincipal = new MyPrincipal(...);
        SUT = new MyViewModel();
    }
    finally
    {
        Thread.CurrentPrincipal = previousPrincipal;
    }
}

ReSharper, for example, handles all the communication work for us. MSpec's ReSharper Runner can hook into the existing infrastructure (that, AFAIK, does not use .NET Remoting).