[flexcoders] Call MXML custom component from AS

[app.developer]

How do you call an mxml custom component from actionscript of another 
mxml application?

In the current application, I import the tester component, then attempt 
to call it my making it a new variable in a function.  When I add the 
child to the stage I get a white background empty object and not the 
red square I'm trying to get into the application.

import comps.tester;

var myNewTester:tester = new tester;


----tester.mxml----

<?xml version="1.0" encoding="utf-8"?>
<mx:VBox xmlns:mx="http://www.adobe.com/2006/mxml"; width="200" 
height="150" backgroundColor="#FF0000">
        <mx:Text text="Test Me"/>
</mx:VBox>


Thank you for your help.
Precia