As you saw previously testing your safelight just by using unexposed paper and a safelight is not going to give an accurate indication of any fogging. A better method of checking for fogging is to expose an exposed print to your safelighting. This way you will have no fogging hidden below the threshold.
A better way. Better than the previous one anyway.
In complete darkness make a good print containing a large area of pale tones, a cloudy sky or something. It doesn't have to be a good picture just a good print with some well rendered pale tones. When you have a print you are happy with make a note of the exact exposure time, like you always remember to do.
Again, working in complete darkness, expose a print identical to the one you already prepared. Once you have exposed your print cover half of it, half of the pale toned area if you can, with a piece of card then turn on your safelight for about seven minutes. That is enough time to expose and process a print in normal conditions. Turn your safelight back off and process your print as before.
When your print is ready compare the light areas on both halves. If both halves are identical things are fine and you are now free to go. If not you will have to move your safelight or reduce its intensity and test again .
Producing a fog free print does not mean you are safe from safelight fogging , it just means you are safe for about seven minutes. If you want you can make a test strip much like making a test strip for a normal print but using an exposed print as you have just done. This would allow you to work out the time your paper can be exposed before fogging will occur.
A couple more things to remember, the values you obtain in the preceding test will only hold true for the type and make of paper you are using at the time and you should always keep the amount of time paper is exposed to safelighting to a minimum anyway.