You might try this change:
<visibilitylabel>Testing</visibilitylabel>
and then reload your project.
Of course, this won't fix it, but it will let you know for sure if the browser is picking up on the changes you make.
Espescially if using IE, I find that, depending on the workstation it is installed on, a <cntrl><F5> will reload with all changes, on other computers you MUST close the entire browser and then re-open the flex page.
Anyway, just a thought as I've had this issue before also.
R_