How to test whether Guaic reagent is working

I have acquired an old bottle with Guaiac reagent which was evaporated in its reagent bottle (10-15 mls). I added alcohol and the reagent dissolved forming a brown solution without precipitate. I don't know if this solution is working (reacting) well or if it has 'expired', hence how can I test it at home pls? Like I am asking how can I test for Lugol's iodine and the reply would be try it on starch or paper and if it turns blackish-blue it is working fine. Thanks

We don't have those Russulas 😭😭😭 Can I apply to some chemical or compound instead? Or fabric or ironmongery material.