Strictly speaking, personas have nothing to do with usability testing. But personas can fill in as users when we're designing, and some teams recruit for studies using attributes of personas they've developed. Connection? I think so.
The Persona Modeler (earlier called "character creator") is a tool that I've been working with and refining for several years to help me define and understand users. I gave a talk about how it works at UPA Boston 2012. Here are the slides. Feel free to download!