Test MEF parts using reflection

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I have an application using MEF and am trying to write integration tests for the Plug-ins.
The code I have is:-

        <pre lang="c#">
        public string Run()
        {
            IFunction IUT = null; string Wanted = "NewUser";
            foreach (Lazy<IFunction, IFunctionData> func in functions)
            {
                if (func.Metadata.FunctionName == Wanted) IUT = func.Value;
            }
            bool res = false;
            res = TestOne(IUT);
            if (res) TestTwo();
            if (res) return "Pass -  NewUser Test";
            return "Fail -  NewUser Test";
        }
        // Normal New User OK
        private bool TestOne(IFunction IUT)
        {
            bool res = false;
            // Set up the VM properties
            var VM = IUT.GetType();
            PropertyInfo prop=VM.GetProperty("UserName");prop.SetValue(prop, "Smith");
            MethodInfo Method = VM.GetMethod("CreateNewUser");
            //...
            //...
            return res;
        }

The IFunction parts are all ViewModels and the Run method finds the correct one OK.
What I want to do is set the UserName property of this VM and then run the Create method

I am stuck on a way to set the VM properties and run the method, what I have does not work.

What I have tried:

Google searches came up with Unit test suggestions but I need to test integration with the rest of the application

Posted 9-Jul-18 7:59am

JohnMeers

Updated 10-Jul-18 15:56pm

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johannesnestler 11-Jul-18 7:06am

It should work by reflection as you showed - so what's your exact Problem with that (it's quite common to set private fields for Tests by reflection).
It maybe the problem that your test doesn't know about your concrete vm-Type?

JohnMeers 11-Jul-18 17:10pm

That's right The test only knows it is a plugin and of type NewUser, I cannot find a way to cast to the actual concrete VM

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Graeme_Grant · Accepted Answer · 2018-07-10T15:57:00

You don't need to use reflection with MEF, you simply Export & Import to share data - the data can exist in a DLL/EXE outside of the main app. So long as MEF can compose, the data will be visible. This is what we did in another MEF Solution[^] where reflection was requested for a plugin system and the plugins automatically load when the DLL/EXE is dropped into the main app's folder.

So, the answer is to create a class to hold your user details in a seperate class (repository), define the Export with a PartCreationPolicy(CreationPolicy.Shared). This will create a static/shared object. Here is an example:

C#

public interface IUserRepository
{
    string UserName { get; set; }
}

[Export(typeof(IUserRepository)),
 PartCreationPolicy(CreationPolicy.Shared)]
public class UserRepository : ObservableBase, IUserRepository
{
    private string userName = "**Not Set**";

    public string UserName
    {
        get => userName;
        set => Set(ref userName, value);
    }
}

NOTE: The above code is not thread safe. I'll leave that up to you to implement if you require that.

Here is the ObservableBase class:

C#

public abstract class ObservableBase : INotifyPropertyChanged
{
    public void Set<TValue>(ref TValue field, TValue newValue, [CallerMemberName] string propertyName = "")
    {
        if (EqualityComparer<TValue>.Default.Equals(field, default(TValue)) || !field.Equals(newValue))
        {
            field = newValue;
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    public bool IsInDesignMode => DesignerProperties.GetIsInDesignMode(new DependencyObject());
}

Now you import the UserRepository:

C#

[Import(typeof(IUserRepository), RequiredCreationPolicy = CreationPolicy.Shared)]
public IUserRepository Repo { get; set; }

... and the user data is now shared whereever the above Import is used:

C#

Repo.UserName = "MainUser";

No reflection coding by you is required as it is all handled by MEF. Enjoy!

PS: Yes, MEF is using reflection so you don't have to! ;)