I was at a talk recently regarding robustness testing. It was separated into parts: Uncontrolled and Controlled.
Uncontrolled involved applying high floating voltages to various pins and logging the results. The circuit in question was an ADC that operated at +/- 20V, and 40V floating voltages were applied at the analog IN pins.
I'm aware that the floating voltage is not referenced to the ground of the ADC circuit, but in what way would would it affect the circuit, and why the need for two tests (controlled test voltages were referenced to circuit ground)?