Do wallbreakers have their damage increased while they are the Rage spell? I know that healers heal is amplified under the effect of Rage. Is there a way we can test it?
Rage spell will increase all troops'es damage and heal, it just won't affect on other spells.
From wiki :
The Rage Spell creates a translucent purple ring on the battlefield that boosts the movement speed and damage of any friendly units inside the ring. In the case of Healers, the Rage Spell increases their healing by a similar amount.
For test you can send a level 5 wall breaker toward some level 7 walls, he will destroy the wall with rage spell but he can't destroy it without the spell.