Testing windows will be opened over the coming days.
If you’re interested in getting into the beta for League of Legends: Dominion then you will want to sign up to the game’s official forums.
As of today, testing windows will be open to a limited numbers of players. New windows will open “during off-peak” hours, each of which will be preceeded by an announcement in the game’s forums to allow you to be one of the first in line.
How many windows will open, and how many days the beta will run for, has not been confirmed.