There's no exactly a test widget button, there's beaconing a widget which is located in the Control Panel in the system info tab. There should be a lightbult icon to the right of the widget and when clicked on the LEDs on the widget should flash.
Another option would be to launch into a show, select your processor, select the output tab, press add mapping, select universes you have nothing mapped to, check widget, and press OK. In the Destination column your widget should be displayed and as long as there's not a warning icon in the License Priority column your widget should be good to go unless it is experiencing a hardware issue.
Once mapping your widget you can then hook it up to a fixture to ensure output works and there are no hardware issues.
