There is no "correct" test. There is only a test that you can use for your own conditions.
Measure the time it takes to make a normal print from package open to into the blix or stop (if open tray) or into the drum. Then place a strip of paper near your safelight, one on your easel, and one at the process site (protected from chemical contamination of course). Then, after exposure to safelight for the time interval measured above, go totally dark and process the 3 strips. Any fog should be compared to a 4th strip that was kept totally dark but is processed with the other 3 in the dark.
Use a 5th strip that was blixed, washed and dried as the base reference.
If there is fog, only you can determine if it is suitable for your purposes. A light tan fog about 0.02 above Dmin is probably ok, but any cyan fog is bad. This is what I have found. And, most safelights cause blue, cyan or purple fog.