I'm partial to an "ordeal" because there is a lot of flexibility here.
Mountain is rooted in the very heart of the Earth but reaches toward lofty heights. She has limitless strength and endurance, but Mountain’s inflexible nature limits her. Mountain is a stubborn and unyielding force, and Mountain magicians are difficult to persuade once they have made up their minds about something.
Here you could make an endurance test. Perhaps surviving in the wild for an extended time or enduring some hardship like a cold clime.
When a Mountain magician makes a plan, she sticks to it. You must make a Charisma + Willpower (3) Test to abandon a planned course of action in favor of a new one. If you fail, you must endeavor to continue with your original plan, even if it means going on alone. Similarly, you must succeed in a Charisma + Willpower (3) Test to proceed in anything without a plan.
Another option would be to have him go on a quest with lots of distractions, testing him to stay on course.