When testing a puppy, observe how it reacts when taken away from its littermates and into a strange portion of the yard. It should not be afraid to leave its pack. It should follow you, explore its new surroundings, and not be easily frightened by new surfaces and textures. Before bringing your puppy home, you should have found a good sport club to join. You should have all the necessary toys and trinkets to make his and your life pleasant.
Socialization is utmost.
It must learn to explore new sights and sounds. Keep in mind however, that our modern world has brought with it many communicable diseases. Keep the pup up to date on all vaccines. A tough task. Many schutzhund clubs are fairly safe, particularly on private grounds.