A Strange Charge Appeared on My AMEX Card (DR ADJ REDIST CADV PRIN), and Customer Service Actually Said This!

I recently noticed a strange charge on my AMEX card: first there was a $100 charge, and then a $100 credit posted. At first I thought it was a refund for something I bought, but when I looked more closely, the charge description showed DR ADJ REDIST CADV PRIN. I had no idea what it was.

So I contacted customer service via online chat. To my surprise, the representative said these were test charges used to check whether the credit card was working properly... I was pretty speechless. Did they really have to test it in such a weird way? Has anyone else run into this before?