flexunit stage null reference

I am trying to test some of my AS classes in flexunit.  Some of the methods reference the stage from components that are passed to it. When I set up the flexunit testing application I use the following code:

core = new FlexUnitCore();

core.visualDisplayRoot = this;

core.addListener( new UIListener( uiListener ));

However, I still get a null reference exception whenever the stage is referenced.  I was wonding if anyone knew what is going on or what I am doing wrong.

Thanks!