A Test Server is a special Game World launched before major gameplay updates. The server may be rotated between Open PvP, Optional PvP and Hardcore PvP.
List of Test Servers
There are two Test Server Game Worlds:
Testa (All people from EU servers in one), located in the United Kingdom.
Testera (All people from USA servers in one), located in the USA.
Test Server's Function
The main function of the Test Server is to find and report bugs in a major game Client Update, so they can be fixed before the Update is put into the normal Game Worlds. Some bugs are content related (e.g. a typo in the words of a NPC), some are technical related (e.g. when you go down stairs you are pushed back up
Test Servers and "Real" Tibia
If you die on a test server, it isn't saved on the normal Tibia servers. You can gain and lose items as well as levels on test servers but your character on the normal server is unaffected, just as items gained and lost on your main character on the normal server won't affect your Test Server character.