I'm learning ActionScript/Flex at the moment, and it's come time for me to start unit testing. My reading shows that there are two main frameworks out there: FlexUnit and AsUnit.
Is there any reason to learn one over the other? Is one, in some way, "better"?
I think it depends on the kind of ActionScript development you're doing. AsUnit has a wider set a supported versions.
FlexUnit looks as though it has a better backing through Adobe. If you're focusing on Flex development (or strictly AS3), I'd probably go with FlexUnit.
There is also fluint, which was created in order to address issues that developers were running into using FlexUnit.
Because of new FlexUnit tooling support in the upcoming FlashBuilder 4 release from Adobe, the fluint project and the FlexUnit project have merged to create a new unit testing suite now dubbed FlexUnit 4.0. The FlashBuilder IDE will support FlexUnit 4.0 at the tool-level. This new tooling support, coupled with some of the great new features of FlexUnit 4.0, make the new FlexUnit the clear choice for unit testing in ActionScript 3 and Flex code.
As a followup to this question, I have been using FlexUnit for the last bunch of months, and it (along with Drew Bourn's awesome hamcrest-as3) has been making me very happy.