Add test showing different args number for async conditionals

Hi,

I suspect that I'm missing some piece of info / misreading docs and unfortunately, I was not able to figure this out by staring into the code either. Could you please point me to the right direction?

The following test shows a different 'signature' for sync and async event conditons. Is this by design? Or should I just use ```-> (*args) { }``` and handle the arguments myself?