A wide variety of tools for creating physical computing systems have been developed, but getting started in this domain remains challenging for novices. In this paper, we introduce test-driven physical computing tutorials, a novel application of interactive tutorial systems to better support users in building and programming physical computing systems. These tutorials inject interactive tests into the tutorial process to help users verify and understand individual steps before proceeding. We begin by presenting a taxonomy of the types of tests that can be incorporated into physical computing tutorials. We then present ElectroTutor, a tutorial system that implements a range of tests for both the software and physical aspects of a physical computing system. A user study suggests that ElectroTutor can improve users’ success and confidence when completing a tutorial, and save them time by reducing the need to backtrack and troubleshoot errors made on previous tutorial steps.