I've never done a diacetyl test. Will do for the next brew.
I've been doing them for a while now after encountering some issues with a NEIPA that fermented out very slowly causing me to rush it into the keg before it had cleaned up the diacetyl.
Pretty easy to do; just take two samples of the beer in sealed containers (I use a couple of these) keep one cool and heat the other to 70degC and hold it there for 10 minutes (I do this on the hob by placing the container in a pan of water). Let it cool down again and then do a smell / taste comparison with the unheated 'control' sample to see whether there is any diacetyl present.