Why are the IEventAggregator.Publish* methods defined as extensions ?

[Maskime]

This is not to criticize or anything,
As I wrote writing some unit tests with Moq on my project, I got an error stating that the PublishOnBackgroundThreadAsync method was an extension method, which could not be mocked.
After a quick look to the extension method, I was wondering what would have prevented you from having those methods defined within the EventAggregator ?
By the way, if someone has already encountered this error and has a quick workaround, that'd be nice to share :)

Thanks for all the hard work anyway !

[vb2ae]

I think there are 2 ways to handle this. There are paid mocking frameworks like TypeMock or JustMock that can mock extension methods. Other option is to mock the eventaggregator class's PublishAsync

    public static Task PublishOnBackgroundThreadAsync(this IEventAggregator eventAggregator, object message, CancellationToken cancellationToken)
    {
        return eventAggregator.PublishAsync(message, f => Task.Factory.StartNew(f, default, TaskCreationOptions.None, TaskScheduler.Default), cancellationToken);
    }