I thought I would cut and paste this from the humane society:
3 to 6 Months: Ranking Period
Puppy is most influenced by "playmates," which may now include those of other species.
Puppy begins to see and use ranking (dominance and submission) within the household (the puppy's "pack"), including humans.
Puppy begins teething (and associated chewing).
4 months: puppy experiences another fear stage.
6 to 18 Months: Adolescence
Puppy is most influenced by human and dog "pack" members.
7 to 9 months: puppy goes through a second chewing phase, part of exploring territory.
Puppy increases exploration of dominance, including challenging humans.
Here is the link from the breeders site i found from this forum actually:
http://yorkiepassion.com/puppystages.htm
Not tons of info....but i wanted to point out that it looks like this whole testing phase may last awhile.