In very general terms, I would say as a minimum an evenly dispersed pattern (no holes in the pattern bigger than 1 sq. in.) centered on your point-of-aim with a minimum of 10 solid hits in the neck/head area on EVERY shot. Obviously a lot depends on gauge and shot size. Since every pattern from a shotgun with the same load will be different, it's good to pattern any given load 3-4 times to determine pattern consistency.
The older I get, the stronger gravity becomes.