FlexBuilder Beta had FlexUnit 0.9 version of FlexUnit swc.
Whenever you create a new test case class or testsuite we will automatically attach the FlexUnit swc. So the ideal way to use the new swc is to place in the location from where the FB picks up the swc so that you can use the feature of the new swc and still get the FB integration feature.
The sample location is <C:\Program Files\Adobe\FB Beta >\plugins\com.adobe.flexbuilder.flexunit_xxxxxx\flexunitframework\version3libs or version4libs
You can bakup the swc available here and place your new swc in this location.
If you have your custom test relatd swc's which you would like to add for your testing, you can place the same also uder this location.
Thanks for the reply. Can I assume that when flashbuilder 4 becomes release, the library that's used will most likely be the newer version? because the newer version is completely different than the old and seems more robust?Thanks
Yes FB will have FlexUnit4 integrated. you can find the details of the feature from http://bugs.adobe.com/jira/browse/FB-18873. We would like to hear from your more about your experience with this feature ( and ofcourse your new expectations also )