How do you get a job in a test kitchen?
I'm by no means an expert on the topic, but it seems to me as though they've usually gone to culinary school or had some other type of food related training.
Which test kitchen are you interested in working in? Which kinds of food are you interested in testing?
This isn't a job, but sometimes Cooks Illustrated subscribers are offered the opportunity to test their recipes.
Cook's Illustrated/America's Test Kitchen has rolling enrollment for kitchen interns. Many of the interns are students in culinary programs, but some are just enthusiastic (and hard working) home cooks. Some of the interns land jobs after their stage time. Here's the link for more info: http://www.americastestkitchen.com/corp/jobs/#job4