I haven’t performed this kind of testing before, but it makes sense it would be “extremely expensive”. As far as I’m aware, the testing methods for this are either on rabbit ears (obvious ethical concerns, and less obvious validity/extrapolation issues) or human subjects. You may need to substantiate that the product is not irritating before comedogenic testing which would add additional cost. These studies involve reapplication over a period of weeks which increases the cost as well.

The term itself is loosely defined and personally, I don’t think it’s worth the cost of testing. Here are some related references that explain better:

https://labmuffin.com/fact-check-how-to-use-comedogenicity-ratings/

https://pmc.ncbi.nlm.nih.gov/articles/PMC8387765/

labmuffin.com

How to Use Comedogenicity Ratings | Lab Muffin Beauty Science

You've probably seen a comedogenicity chart like these ones (and the one further down the page) before, rating different ingredients on their ability to cause pimples. Supposedly you check the…