How can I start the NGX with a random failure activated before the preflight checklist?

Ouch, that hurt my brain trying to understand you.  How is a failure random and active at a preset time?

I'm mean, "an active random failure" before the preflight checklist... so that we could consult the MEL to see whether that failure was allowed or not for the flight... would give life for the preflight check (flow), because we know there could be some failures...