It's almost impossible to detect an adulterant unless you know what adulterant you're looking for.

There are an awful lot of possible adulterants out there too.

Therefore, testing is a bit of a losing game. Instead, developed nations like the US require record keeping (ie. you need to keep a list of suppliers for each batch, and sometimes samples of each batch), and the court system allows someone to sue for a lot of money after the fact if a poisonous adulterant was found.

The risk of being sued is what keeps most food safe.