I have both CGC & TDI on all of my dogs.
If you want more information on the CGC (Canine Good Citizen Test);
http://www.akc.org/events/cgc/index.cfm
If you want more information on the TDI (Therapy Dog International):
http://www.tdi-dog.org/whatdo.html
I personally recommend that everyone that has a "pet" dog should really get their CGC testing done. It can help in so many ways, even if you thought the test itself was a breeze. There are a lot of appartment complexes and housing developments in some cities that now only let you live there w/ your pet if you've been tested. Further, airlines are talking about it being a requirement to fly w/ your pets (although, I don't think that'll go through myself) and so on. All in all, it's certainly worth the $5-$10 testing fee imo.
If you have any further questions, please feel free to PM me.
