Nexon announced in its Tree of Savior 1st CBT operating policy that "The testing progress cannot be broadcast through online streaming".
The reason is simple and understandable. It's going to be first closed beta and Nexon Korea doesn't want to advertise or promote the unfinished game or negatively influence the audience by the game in development. Focus of the CBT must be to determine the direction of the game through feedback from the testers.
However and that is a little bit surprising you will be able to upload and watch videos on Youtube or show screenshots.
1st CBT takes place from January 15 - January 18 2015 and 3,000 Koreans should participate.