There is described an electronic device testing system for testing an electronic device having a substrate on which is printed a metamaterial structure using an ink. The electronic device testing system generally has: a terahertz radiation emitter configured to emit an incident terahertz radiation beam to be incident on the metamaterial structure of the substrate, the incident terahertz radiation beam having power at least at the terahertz resonance frequency of the metamaterial structure; a terahertz radiation receiver configured to receive an outgoing terahertz radiation beam outgoing from the metamaterial structure and to measure an amplitude of an electric field of the outgoing terahertz radiation beam at least at the terahertz resonance frequency; and a controller configured to determine a conductivity value indicative of a conductivity of the ink based on said amplitude of the electric field of the outgoing terahertz radiation beam.