The community test environment (CTE) is a group of servers that maintain and hold the game elements which aren’t yet out for the public. In simple terms, they are test servers. On the official website of Battlefield 1, DICE made an announcement on the CTE.
It looks like the CTE will be set-up for the first person shooter game on PC. This CTE will house new features, improved/changed content, and experiments that aren’t yet made publicly available.
The entire purpose of bringing up the CTE is to make the public provide some feedback on the game, so they can do the necessary changes before launching a new update.
DICE is going to choose only selected community members and Battlefield 1 professionals, and give them the access codes for entry into the CTE. The others can register and wait for a chance through the Battlefield companion app.
The game’s CTE is now available for PC. DICE doesn’t have any confirm plans on bringing the CTE to the consoles.