def next_round_turn(game_state):
    """ Takes the round and turn from the game state dict and returns
    the round and turn of the next step in a dict.

    Returns
    -------
    dict { 'round' , 'turn' }
        The updated round and turn

    Raises
    ------
    ValueError
        If gamestate['gameover'] is True
    """
    if game_state['gameover']:
        raise ValueError('Game is already over')
    turn = game_state['turn']
    round = game_state['round']
    if turn is None and round is None:
        turn = 0
        round = 1
    else:
        turn = turn + 1
        if turn >= 4:
            turn = turn % 4
            round = round + 1
    return {'round': round, 'turn': turn}
