Check if unit is still channeling?

Can somebody please post a trigger that checks if a unit is channeling a spell so that a dummy can continue channeling a dummy spell? Im trying to make the volcano ability, but have a dummy channel the ability, so if the caster stops the dummy would stop channeling.

Detect when the unit order is different from the spell one with a looping function (timer).

im not sure i completely understand. you want it so that when the caster stops casting your dummy stops too?

If this is what you need, then you don't have to detect if the unit is still channeling the ability, instead you should detect when the unit stops channeling it. There is a trigger event that does just that.