Is there a way to test Flash ActionScript scripts without having Flash installed and running them inside a swf?
While this may be a technicality, you could run actionscript code in the Adobe AIR runtime, as opposed to the Flash Player. Deep down, though, there's still a swf involved in the creation of your AIR app.
You could download the Flex SDK for free and use that, or use the Flex Module for Apache and IIS, if you need to check scripts online. I'm guessing it's what sites like Wonderfl use.
Otherwise, for simple things like
function add(a, b){return a+b;}
You might as well adjust lint or find something similar.
I would highly recommend flash develop. It works with flex sdk. it actually runs more smoother too. Not only this but it makes a far better IDE then flash cs4. it has a far better intellisense, and it also does intellisense for customs class. I have flash cs4 and I still use flashdevelop