What is your draw length!  Generally, I think the arrow length should be long enough for the point to be clear of the back of your bow and your grip hand at full draw.  As for a spine tester, as TimBo said, a 2 lb weight, and set your rests 28" apart, you can fudge just a bit on that.  If you have a known spine arrow, put your weight dead center and mark the sag point for reference.  Most shafts you buy will be in a 5# range, such as 40-45#.  
Hawkdancer