So if you find you ARE that friend, presumably you'd have no fear of stepping in front of that gun barrel yourself for a few million flips right afterwards. I mean it's pretty convincing proof. Then you get to see the confusion in each other's face!

Though you're both more likely to end up mopping your friend's blood of the floor.

On the whole, I think a good friend probably doesn't let a friend test the Quantum Theory of Immortality.