Well I feel stupid!
The answer to my question is that I left out the name of the Mediator when registering it!
The proper code should be:
[Test]
public function facadeCanRegisterMediator():void {
if(!Facade.getInstance().hasMediator(NewReelMediator.NAME)) {
Facade.getInstance().registerMediator(new NewReelMediator(NewReelMediator.NAME));
}
assertTrue(Facade.getInstance().hasMediator(NewReelMediator.NAME));
}
which of course... passes. Events have nothing to do with it. There is no event which is fired when a mediator is registered.