Feedback and a changelog is given for each extension in it's announcement thread, or bugs can be mentioned in TCE Bugs. Many extensions are updated at a rapid pace, mostly to keep up with the current upstream version. As a protocol, "TESTING" is to be added to the description field of all new extensions.
But to be honest, in the beginning I don't think we had any idea how rapid the pace of extension development would be. And moving extensions out of the TESTING zone is something that has fallen behind. With some extensions being updated every few weeks, if the TESTING label was removed after positive feedback, the extension would go right back into TESTING upon the next update which would happen very quickly.
With our fast pace of extension development, I will admit that I am not sure on what would be a sane process for dealing with the TESTING label and when extensions would move out of it.