I've spent a lot of time in the debugger over the last few days trying to figure out how to unit test struts 2 actions with the Interceptor stack so that validation and results configuration etc. were also tested.

I wrote a unit test helper class and posted it and a description here Unit Testing Struts 2 Actions [1] hopefully others will find this helpful.

[1] http://glindholm.wordpress.com/2008/06/30/unit-testing-struts-2-actions/