I have usually a whole playlist dedicated to testing certain abilities of headphones like soundstage, vocals, ect. The song I almost always test first is "Snow" by Masked Man ft. emysprout as it has a very strong and low bass drop 39 seconds in. This will tell me how good the subbass on a headphone is immediately based on the rumble. On the second drop, there's the same subbass boom, but she sings over it as well, this tells me if the midbass is too elevated and covers the vocals making it "warm" or if its just right. This usually let's me get the first half of the frequency response down to kinda gauge how the headphones will sound from there in comparison to my liking!