I don't believe that there is any requirement to have small parts tested by an outsite lab. You can go to the cpsc website and search for small parts and you can find all the info you need as to diameter, length, etc. I also believe you can buy a small parts tester. It is not a brain drain test, if the part can be detached thru normal wear and tear of the under 3yr old or it is a seperate piece that they can get into their mouth, and it will fit into the tube (which is the size of their throat) then it is too small.
What are you making?