Just to further clarify,
A reverser unlocked indication on every a/c I have worked on does not require the engines to be running (tho' many types do require engines running (or a maintenance over-ride) to operate the reversers). If electrical power is applied and a translating sleeve/deflector door is unlocked then an amber REV indication will show.
Power checks are not carried out prior to each flight (no mags to worry about & no need to get the engine oil up to temp)