I haven't run a game yet on roll20 (organizing one right now though), and I was looking for a way to test in-advance if my camera works with tokbox. I searched the forums and didn't find one, but tokbox has one:
<a href="http://www.tokbox.com/opentok/api/tools/tutorials/helloworld.html" rel="nofollow">http://www.tokbox.com/opentok/api/tools/tutorials/helloworld.html</a>
read the instructions beforehand (i.e. mute your audio before starting up, otherwise you may get bad feedback).