test_count_unknown_squares

    string test_board_3[] = {"XOXOX",
                             "--OOX",
                             "---XX",
                             "--O-X",
                             "--O-X"};
    int size_3 = 5;
    read_board_from_string(board, test_board_3, size_3);
    cout << count_unknown_squares(board, size_3) << endl;
    
    string test_board_5[] = {"XOXOX-",
                             "--OOX-",
                             "---XX-",
                             "--O-X-",
                             "--O-X-",
                             "--O-X-"};
    int size_5 = 6;
    read_board_from_string(board, test_board_5, size_5);
    cout << count_unknown_squares(board, size_5) << endl;