As we all know, creating applications is loads of fun, but since we are not perfect developers, we do tend to create applications with bugs in them (but you know, that doesn't happen often :) ). And because of that, we need to properly test our applications, including our Flex/AIR applications. I have mentioned various testing frameworks many times on my blog, but just came across this list of 10 unit testing frameworks with a brief description to each.
Not on this list if RIATest, an application used to perform recording and playback of Flex/AIR applications, which is what we use at my company.
In any case, research and use the one you fell is best for the job so that you can deliver the best applications out there!