Does the world become the entity at that point? Or the game state? The reason I ask is because the System object takes an Entity as an argument. If the Player is a component it leaves me unsure what is supposed to become the Entity. I'm trying to build the mental model of how all the pieces will fit together.
the world is a not an entity. it represents the game loop. The (S)ystem needs to be updated/changed. they current System was only to get that test to turn green.
the player component will contain (ManaPool, Hand, Graveyard, etc); then we can create inherited component of HumanPlayer and AIPlayer.
I also think that each card should be a separate entity.