On the 4 engine Lockheed JetStar bizjet, we would check the thrust reversers by extending them during taxi, we would only do this the first flight of the day. A lot of times to save fuel we would taxi out on 2 engines and when we reached the check reversers part of the taxi check list, we would hold off continuing the check list until we started the remaining 2 engines and tested the reversers.
We could extend all the reversers with only # 2 engine running because #2 engine powered the #1 hydraulic system, which supplied hydraulic power to all the reversers. But part of the test was to see engine rpm increase when the reversers were extended so we waited until all the engines were running.
On the ground, we used the electric hydraulic pump to power the #1 hydraulic system so we could extend and retract the reversers as needed. Part of the preflight was to bleed all the hydraulic pressure off, including all the accumulators, both the brake and reverser accumulators held pressure because they were designed to operate the systems in case of a hydraulic failure, so the only way to bleed pressure off was to operate the brakes and reversers. We could get about 5 brake applications and extend, retract and partially extend all 4 reversers just on full accumulator pressure.
On the JetStar some operators on a windy day would extend the reversers while the aircraft was parked to prevent the wind from blowing up the tailpipe. If I remember correctly there was a 30 knot wind restriction when starting the engines with the wind blowing up the tailpipe, it was an approved procedure to start the engines in this wind condition with the reverser extended and retract the reverser once the engine reached idle.