Cool Software: AsUnit
AsUnit is an Open-Source, Unit Test Framework for Macromedia Flash ActionScript 2.0. It is fully integrated into the Macromedia Flash MX 2004 Professional IDE, but it’s primary features require minimal interaction with the Flash Environment.
I have not tried the software as of yet, but porting JUnit to ActionScript 2.0 and Flash can only be a good thing. The website has a link to Colin Moock’s site where he says good things about AsUnit — that’s good enough for me.