Mad engineers with super engineering powers at that. I work in robotics -- in real life, the amount of effort necessary on the part of many engineers, some with Ph.D.s, to get even a simple robot like one of our AUVs assembled, integrated, and functioning with acceptable reliability is phenomenal. Yet Dr. Robotnik can build a whole robot army numbering in the thousands of many different types, a fleet of airships to deploy them from, and a chaos-emerald-powered world-shattering satellite -- all by his lonesome, all over Sonic's summer vacation, and all without having to worry about malfunction except via high-speed impact by blue hedgehog.
I believe you've uncovered one of the great flaws of standard testing procedures. The tests cannot test anything the developers don't think up. Robotnik has a big blank space where a blue hedgehog should be.
Despite his monumental engineering feats the guy didn't account for some pretty basic deficiencies. If I were him I would set up a test jig consisting of a cannon which fires spiked cannonballs at high speeds, and make sure my killing machine's armor could withstand at least that before deploying it. I would also take care that it never enters a failure mode that involves exposing its power core, CPU, or other delicate parts; and I would license Tony Stark's arc-reactor technology to power it, as the very rare mystical gems I would otherwise need tend to be either highly sought after by ambitious hedgehogs or guarded by fierce echidnas who would stop at nothing to ensure their safety and sanctity.
