Apparatus and methods for non-contact testing of electronic components printed on a substrate (3) are provided. Test circuits (11) are printed on the substrate (3) at the same time as the desired electronic component. The test circuits (11) are all optical and include a first portion (13) for providing electrical energy for the test circuit (11) and a second portion (15) for generating a detectable optical signal that is indicative of at least one electrical property of the electronic component. The test circuits are used in real time and minimize the production of unusable scrap in the printing of such products as ePaper.