I can't understand why it ISN'T standard practice for the engineer who did the work to come and prove its integrity by riding in the aircraft.
If he doesn't want to sign for it, neither do I!
Likewise the individual writing a flight related snag in the book. I can't recall the number of "no fault found" ground runs and test flights that we pursued after they are put in the book. We changed our procedures, so that whoever writes the entry, is responsible for, at least, the first run or flight in the troubleshooting process so at least there was some possibility of replicating the deficiency.
Our number of wasted hours dropped, availability and expediency in resolving genuine snags increased dramatically.
And the person fixing it goes along too. Keeps everyone honest!