You would still have to test against Harmless...
This is going to sound really weird, but Immune to Influence models still have to test against things like Harmless, Terrifying, and Pitiful... The reasoning is best explained by Ratty (one of the Rules Marshals on Wyrd's forums, his word is law).
Ratty wrote:The thing to remember is that you can be multiple things at once in a game.
Example 1. If you get targetted by a spell using your Wp to resist.
You are the Defender, as there is an Attacker (read the rules for when something is an Attack).
Your in a Wp Duel, As you are using the Wp stat.
Your Resisting a magical Attack, as the Defender in a Magic duel counts as resisting.
Example 2. If you are in melee range of a terrifying model.
You are not Defending, as there is no Attacker (no model is targeting you model, nor is it an aura or pulse that does damage).
Your in a Wp Duel, As you are using the Wp stat.
Your in a Morale Duel, as all terrifying duels are Morale Duels (note not all duels involving Wp are Morale Duels)
Immune to influence says you Need to be Defending & You need to be in a Wp Duel. So if you check these two criteria you will see in Example 1 you will be Immune but in Example 2 you won't be as you are not a Defender.
So a model with Immune to Influence has to do 2 things, 1) Is this a Wp Duel (a duel in which he uses his Wp stat) and 2) Is he the defender? Since Harmless doesn't target, there is no attacker and defender. Also, it's a simple Duel, so all you have to do is meet the number, rather than beat it.
Hope that helps
