In such limited quantities is it really a problem - do customs really try and enforce the Dangerous goods rules? I’m sure they are more interested in contraband than a few mls of testing solution – yeah they could easily inform you that you shouldn’t take it on a flight, but it’s too late.
These kits are shipped worldwide – very rarely do they get shipped as dangerous goods, they are sent in the regular post, with no mention to the contents.
In defence with customs my argument would be, I received it via airmail – I don’t know what the stuff is but I assumed it was safe. It would be a very tough/pissed off customs officer that took it further, don’t you think?