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)

Actually, engine oil needs to be within limits before take off, but that is usually done by the time you reach the runway, except in extremely cold climates with a cold soaked engine.

As previously stated a thrust reverser sleeve not in the fully stowed position will provide a warning even if the engine is not running. It's always good to debrief the inbound MD-11 crew only to find the dreaded amber "U/L" displayed in the middle of the #2 engine N1 indicator:{

All kinds of reversers (just like planes) and all kinds of logic and safe guards.

However, with the lessons learned in most transport jets, an unwanted reverser deployment can be bad news. Thus the need for weight on wheels switches, reverser unlock switches and FCOM manuals of what to do.

Simply as one poster has already said if below V1 abort, if above V1 bring the engine to idle ... and leave it there. (one guy didn't and upon reapplying thrust the reverser deployed)

Most protection logic in the design should auto-command a stow of the reverser for a simple unlock light warning if there is no weight on wheels. However its still up to the pilot to command the engine to idle.