<p>Are there any unit testing solutions for Flex? or actionscript 3?</p>

<p>If so, what are their features? Any UI testing abilities? Functional testing? Any pointers, examples, libraries or tools that you can share?</p>

FlexUnit is pretty awesome -
http://opensource.adobe.com/wiki/display/flexunit/FlexUnit
Also ASUnit -
http://asunit.org
They are both pretty similiar and both haven taken quite a bit from frameworks like JUnit.
FlexMonkey (
http://code.google.com/p/flexmonkey/
) although I haven't used it myself seems to do UI unit testing.