I first became involved with formal usability testing at Education Networks of America (ENA). Previously, I had provided usability feedback informally to developers during the documentation process.
A large part of the usage-centered design process I introduced at ENA was iterative usability testing. I developed test scripts, coordinated the tests with the participants and the design teams, and summarized test results.
Here are some sample deliverables from usability testing and usability work I've done: