Strictly speaking, "pushing the envelope" is testing a system to find out where its limits actually are.
Test pilots routinely push the envelope
(in fact as far as I know the term is aviation slang) so that a set of normal limits can be defined for a new aircraft, but even a test pilot doesn't spend much time outside the envelope, because outside the envelope is where the plane doesn't fly, and if you don't get back inside the envelope real quick, you're gonna auger in.