Had a 45 minute long informal chat with the guy who would be my line manager, we talked through my CV and experience, technologies I had used and so on, then we talked about the company, what they do and how they test. Toward the end another chap came in and gave me some Python code to review, prompting me to point out what was wrong with it. It contained everything from glaring logic errors to subtle style issues, and I probably didn't see everything, but it was a positive experience. They seemed like nice people and I would have worked there if there weren't issues with my agency.