The Test SIG is a fictitious group, meant only to demonstrate this server to SIG leaders.
The Test SIG never meets in person. You would be foolish to subscribe to the Test SIG Calendar.
The "test-announce" mailing list is for vital Test SIG news, issued by the group's leader.
Note that the leader can also deputize individual subscribers, enabling them to issue announcements by themselves.
The "test-talk" mailing list is for general discussion among all subscribers to the list.
Note that because "firstname.lastname@example.org" is itself subscribed to "test-announce", announcements will automatically go to both lists.
Supposedly, the mail server is still smart enough to send only one copy of a message to a given address, even if that person is subscribed to both.
The "test-secret" mailing list is private.
Note that only subscribed members can view the list's archives, upon supplying an e-mail address and password.
Also, the group leader can individually approve or reject each subscription request.
The group leader of the Test SIG can reconfigure all this by signing in as group name "test".
The Pi Volunteers board on the TCS is a good place for group leaders to compare notes.