With such a great job posting ddl and sample data I think you deserve a complete answer. I wish more people would make their posts so easy to work with.

declare @Top int

set @Top = 2

;with cteCount as

(

select TestGroup, TestData, ROW_NUMBER() over(partition by TestGroup order by TestData) as RowNum

from TestTable

)

select * from cteCount

where RowNum <= @Top

Now all you have to do is change the value of @Top and the number of rows per group will change. It will also work if @Top specified finds fewer rows for any given group. Say you added a group 'C'.

INSERT [dbo].[TestTable] (TestGroup,TestData) VALUES ('C',5)

It will find and return only the 1 row for that group.