select
    OrderID,
    Items,
    GroupID,
    RunningTotalInGroup,
    SUM(IncrBasket) OVER(ORDER BY groupID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as BasketID
from (
    select
        OrderID,
        Items,
        GroupID,
        case lag(groupid) over (order by groupid)
            when GroupID then
                case
                    when SUM(items) OVER(PARTITION BY groupID ORDER BY groupID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) >= 10 then 1
                    else 0
                end
            else 1
        end as IncrBasket,
        SUM(items) OVER(PARTITION BY groupID ORDER BY groupID ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) as RunningTotalInGroup
    from #TestTable
) Rslt