Believe it or not, "Yorkshire Terriers for Dummies" is a very good book. You can find it on amazon:
Yorkshire Terriers For Dummies - Kindle edition...
The link to the Wisdom Panel DNA test is here:
Dog DNA Test, Dog Breed Test - Wisdom Panel Canine DNA Testing | Wisdom Panel . They send you a test kit. You take a cheek swab from your dog, carefully following the instructions, and mail it in to the company. It takes three weeks or so to get the results.
Partis and Biewers share the same origins, but Partis are more like American Yorkshire Terriers, and Biewers are more like European Yorkshire Terriers. Biewers are supposed to be bred only with other Biewers, but Partis can be bred back to Yorkshire Terriers. Biros are chocolate-colored Biewers, and Gold Dusts are yellow-colored Biewers.