I still think the most effective test for a shotgun is the old cheese cloth tied between two sticks at the appropriate height and the shooter stands back, quickly mounts the gun and fires. After awhile a black splotch will appear on the cheese cloth noting where the shotgun is throwing the majority of its pattern. Either, high, low, to the left or right then the shooter can compensate or if dissatisfied can 'cook' up another recipe to see how that patterns.
All the best