I test rums with a hydrometer and include the info in my rum reviews. The objective of this is not to be critical of any specific rum/brand, but to put information into the public domain regarding additives in rums to assist consumers in knowing what is added to their drinks and therefore whether or not the price tag of a bottle is justified. It is not a scientific test carried out in a laboratory nor does it definitively prove that additives in rums exist.
I followed Johnny Drejer’s guidelines, as stated on his Drecon web site.
I would also like to say thanks to Wes who originally suggested to me to get a hydrometer for testing rums, back in 2016.
UPDATED: October 10th, 2017
Here are some links to other hydrometer tests: