It's not a stupid question. It's a good question. OTO test kits test for chlorine/bromine (you have no bromine, that's for people who use bromine instead of chlorine) and pH.
There are basically 3 ways to test for Stabilizer, AKA, "CYA" for Cyanuric Acid"
1) Take a sample to a pool store.
2) Some of the more expensive strips by Hach and LaMotte have a CYA test pad, but aren't very accurate.
3) Get a CYA test. Most pool stores don't sell them but some do. Better still, go to Watermom's Sig and click on the link to test kits. Order the Taylor K-2006 or K-2006c test kit from Amato (it helps support PF a little). That has the CYA test. The classic CYA test is the "Black Dot" test: You pour treated pool water into a vial with a black dot at the bottom. The chem makes the pool water cloudy. When the black dot cannot be seen from the top of the vial, it will show a CYA level on the side of the vial.

Carl