1. Summon any entity that can be hit by arrows and are affected by instant health and instant harming potion effects (or use another player as a dummy).

2. Fire Arrow of Harming/Healing at full charge at the test dummy.

3. Observe that the arrow has done 6-10 damage, which is the same range of damage that a normal arrow does when fired at full charge.

The potion has had no effect on the hit entity, probably because the effect is attempting to be applied while the entity is hurt by the arrow and cannot do so.