1. A method involving non-destructive testing of a sample device having a specified function in the context of electronic circuitry, comprising: applying one or more off-normal stimuli to the sample device, wherein each off-normal stimulus is a periodic electrical signal, devoid of logical information, that is applied between a power pin and a ground pin of the device while each other pin is electrically connected to a power pin, is floating, or is biased at a constant voltage; under each of the one or more off-normal stimuli, measuring at least one power spectrum at a selected pin of the sample device, wherein the measured power spectrum represents a response of the sample device to the respective off-normal stimulus, and wherein each power spectrum is taken over a multiplicity n of spectral bins; performing a Principal Component Analysis (PCA) on each power spectrum, thereby to obtain a respective set of principal components of each power spectrum; for each power spectrum on which a PCA has been performed, selecting at least one subset of the set of principal components, wherein the subset consists of fewer than n of the principal components; comparing the subset or subsets obtained from the respective power spectra on which a PCA has been performed to stored reference data, thereby to obtain a comparison result, wherein the stored reference data include representations in terms of principal components of one or more reference populations of devices having the same specified function as the sample device; classifying the sample device relative to reference populations, wherein the classification is based at least in part on the comparison result; and placing the sample device in a batch of devices confirmed for further processing if the sample device is classified as similar to a reference population of acceptable devices, but placing the sample device in a batch for disposal if it is not classified as similar to a reference population of acceptable devices.