IMessengerExtensions.Send blocks unit testing

[mikeKuester]

Hello,
I'm migrating a legacy app from MvvmLight to CommunityToolkit. Most parts are easy to handle, but now all unit tests which check the IMessenger calls fail, because of the IMessengerExtensions which use the internal Unit type.

I use .NET Framework 4.8.x and Moq for unit testing.

There is a messenger send in a method:

Messenger.Send(new NotificationMessage(Notifications.MyNotification));

And the unit tests for the method contains something like this:

msgrMock.Verify(
    p => p.Send(It.IsAny<NotificationMessage>()),
    Times.Once
);

The extension method Send<TMessage>(this IMessenger messenger, TMessage message) uses the internal type Unit, which I can't use in my units tests to see if a mock has the right invocations.

dotnet/src/CommunityToolkit.Mvvm/Messaging/IMessengerExtensions.cs

Line 422 in 657c697

public static TMessage Send<TMessage>(this IMessenger messenger, TMessage message)

    public static TMessage Send<TMessage>(this IMessenger messenger, TMessage message)
        where TMessage : class
    {
        ArgumentNullException.ThrowIfNull(messenger);
        ArgumentNullException.ThrowIfNull(message);

        return messenger.Send(message, default(Unit));
    }

I can't write a working unit test:

msgrMock.Verify(
    // But the type Unit is not accessible
    p => p.Send(It.IsAny<NotificationMessage>(), It.IsAny<CommunityToolkit.Mvvm.Messaging.Internals.Unit>()),
    Times.Once
);

Why is it not possible to use a public type in the extension method for the TToken?

The extension method should make it easy to use the Send method if you don't need different channels. However, the current implementation prevents this when I want to test my code. Or did I miss here something?

Thanks,
Mike

Update: It's not only the send method, all methods have the same problem.