Prism - how to test ShowDialogAsync (Extension method being called instead of class method)

Question

As we know, if there are method in a class and extension method with the same signature, the method in a class should be called instead of extension one.

So my problem is the next. I'm trying to mock IDialogService from Prism.Services.Dialogs. My goal is to have a mock for ShowDialogAsync method which could be tested (static/extensions methods couldn't be mocked).

The signature of ShowDialogAsync method is:

namespace Prism.Services.Dialogs
...
public static Task<IDialogResult> ShowDialogAsync(this IDialogService dialogService, 
   string name, IDialogParameters parameters = null);

So I created class MockDialogService:

namespace LoadApp.Core.Helpers
{
    public class MockDialogService : IDialogService
    {
        public void ShowDialog(string name, IDialogParameters parameters, Action<IDialogResult> callback)
        {
            //throw new NotImplementedException();
        }

        public Task<IDialogResult> ShowDialogAsync(string name, IDialogParameters parameters = null)
        {
            Debug.WriteLine("ShowDialogAsync");
            IDialogResult res = new DialogResult();
            return Task.FromResult(res);
        }
    }

    public class DialogResult : IDialogResult
    {
        public Exception Exception { get; set; }
        public IDialogParameters Parameters { get; set; }
    }
}

and use it in the test:

_dialogService = new MockDialogService();
...
var viewModel = new ViewModel(_dialogService);

During debug session I see dialogService in the model is the instance of my class MockDialogService. But ShowDialogAsync method from my class doesn't call, it is extension method still called. What I missed? Thank you in advance.

Answer 1

After spending some time I found the workaround.

I created my own extension method:

public static class MyDialogServiceExtensions
{
    public static Task<IDialogResult> ShowDialogAsync(this IDialogService dialogService, string name, IDialogParameters parameters = null)
    {
        if (dialogService is MockDialogService myService)
        {
            return myService.ShowDialogAsync(name, parameters);
        }
        return IDialogServiceExtensions.ShowDialogAsync(dialogService, name, parameters);
    }
}

and changed calls

await dialogService.ShowDialogAsync("MyDialogPage", parameters); 

to

await MyDialogServiceExtensions.ShowDialogAsync(dialogService, "MyDialogPage", parameters);

P.S. I changed the question name to help others who have the same problem to find this topic.