[Spell] Triggering Help

I been working on this spell since a few days ago. Its a spell that works like a defensive device against spells that were casted on you. It takes the damage of the spell casted on you (enemy spell) and reduces it damage or stops that spell.
The problem is that I can't find anyway to find the spell's damage.

I figured there are 3 ways.

1. Put every damage spell in a var, their dmg, and the level. (most accurate)

2. Find how much health was lost (inaccurate because the hero regenerates)

3. Find how much health was lost on a dummy (inaccurate because the dumy can regenerate.

Is there any other way to figure out damage?

No, there is unfortunately no other way.

ehh, on the third alternative...
if you use a dummy unit, you can always take away the regeneration from it ^^

After a test, the hero DOES NOT Take the full damage of the spell. Now, unfourtantly, it screws everything up. If a storm bolt did 100 dmg, the hero would only take 75-90 dmg. It could be the armor of the hero reducing the spell damage or the hero armor.