Typically, a "turn" in a CCG isn't a "turn" in the traditional game tree usage of the word, but a sequence of many AI turns of different types.
Taking Magic: the Gathering as a reference, every time a player passes priority to the opponent to answer his move it is one turn in the game tree, even if the other player's move is doing nothing (which in many cases is the optimal choice). Some of these turns are special actions (e.g. declaring attacking and blocking creatures), some are game state changes without player decisions (e.g. resolving spells and abilities, combat damage steps, state based actions) and some consist of composite moves (e.g. playing mana abilities as you play a spell or ability, or stacking several spells and abilities without passing priority).
Edited by LorenzoGatti, 03 August 2014 - 11:48 AM.