To test the kit, just urinate in the ammonia test tube, and see if any ammonia show up. If none does, your kit may be bad.
I also think that a turtle usually produces a lot of waste, even for a 30G. API's test shows 5ppm Nitrate as a first indicator. If you shut off the lights for 2 days, and then re-test, you should get nitrates since the algae can't use the nitrates without light.