Stop in for a cup of coffee

Quick question.... how to tell if a thermostat is a 2 way or 1 way? Like how to tell if it will puke coolant into a tank, then pull it back in as it cools vs just puke on the ground if overcoming cap pressure then be low on fluid?
Don't know the answer to your question, closest thing I've experienced is changing daughters Jeep Cherokee from a closed sytem to an open system. It used to blow the lid off the coolant tank iirc