As long as no soil sterilants were applied when the synthetic was laid (this is not commonly done...but has been done to some lawns to prevent weed growth), the soil may not require much preparation beyond the "normal/standard" soil prep for new turf:
1. tillage, to incorporate 3 cubic yards of compost or other good quality organic matter per 1000 square feet.
2. Rock/debris removal
3. Smooth/level and firm the surface for sodding

There is no standard test for the presence of soil sterilants. If there are trees growing i the landscape and they are healthy, this is a good indicator that the soil is OK for planting turf.

Let me know if you have any further questions.

Tony Koski