使用AppDomain为单元测试提供应用程序调度程序

Question

Problem: Application.Current is null in a class when running a unit test.

Approach to resolve: Create an application domain that will run my test class. The application domain will provide a dispatcher for my test class.

Code example:

        MyClassInTheAssembly myClass;
        string path = @"C:\\pathToTheDll\\MyAssembly.dll";
        path = path.Replace(@"\\", @"\");
        AppDomainSetup setup = new AppDomainSetup { PrivateBinPath = path };
        AppDomain domain = AppDomain.CreateDomain("MyDomain", null, setup);

        myClass = (MyClassInTheAssembly)domain.CreateInstanceFromAndUnwrap(path, typeof(MyClassInTheAssembly).FullName);

The myClass object can be used to unit test any public methods that use Application.Current.Dispatcher.

I receive the following error when executing a unit test on myClass:

Constructor on type 'MyAssembly.MyClassInTheAssembly' not found.

This error is generated while invoking domain.CreateInstanceFromAndUnwrap() method to create an instance of my test class.

MyClassInTheAssembly constructor has two required parameters. Is it possible to create an AppDomain instance of a class with parameters?

UPDATE Thanks to user779967 for pointing me in the right direction. The answer to my question above is to use a method override for AppDomain.CreateInstanceFromAndUnwrap(). I tried using the method override to create an instance of my test class using AppDomain:

        object[] parameters = new object[2];  // object array to pass my required parameters.
        parameters[0] = container;  // Required constructor param for myClass.
        parameters[1] = eventAggregator;  // Required constructor param for myClass.
        myClass = (MyClassInTheAssembly)domain.CreateInstanceFromAndUnwrap(path, typeof(MyClassInTheAssembly).FullName, true, BindingFlags.Default, null, parameters, null, null);

The idea was to use this method override to pass my required parameters to the instantiation of my test class. Then I could use the test class derived from AppDomain which provides a dispatcher thread for all my unit tests.

I received the following SerializationException when executing this code: Type is not resolved for member 'Castle.DynamicProxy.Serialization.ProxyObjectReference,NSubstitute, Version=1.6.1.0, Culture=neutral, PublicKeyToken=92dd2e9066daa5ca'. This is because I am required to use NSubstitute for unit testing my container and eventaggregator classes. The AppDomain method is looking for an exact parameter type match of IUnityContainer and IEventAggregator for my constructor parameter types, not NSubstitute.

I gave up my attempts to use AppDomain to instantiate my test class for unit testing. I decided to handle Application.Current within my test class method as follows:

        var dispatcher = Application.Current != null ? Application.Current.Dispatcher : Dispatcher.CurrentDispatcher;

        if (dispatcher.CheckAccess())
        {
            do something....
        }
        else dispatcher.Invoke(DispatcherPriority.Normal, (Action)(() => CallMethodAgain())); 

When running my code in production, Application.Current should never be null. When running my code for unit testing, I use Dispatcher.CurrentDispatcher to create a dispatcher from the executing thread.

If someone out there has a nice implementation for using AppDomain to instantiate a class for unit testing, I would love to see it!

Answer 1

Check this overloaded version of CreateInstanceAndUnwrap

http://msdn.microsoft.com/en-us/library/dd387239.aspx

Seems that you will need to create an array of type object[] and fill it with your constructor arguments.