Hi,
I’ve tried to upload a fake TOC to a release on test.musicbrainz.org, therefor changed Picard’s Server Address to the test db and started a manual lookup. I was astonished as there was all the data I entered just yesterday (“How did they do that?!”). But then I looked at the address bar and I realized, I’ve ended up in the real world. 
After changing to test.musicbrainz.org (now really), there was no further problem and everything went as planned. But in worst case I might have added a fake TOC to an existing release without knowing.
Or isn’t test.musicbrainz.org supported by Picard? I’ve seen that beta… is available in the pick list while test… is not. (Though I thought, I had tested it successfully… 
)