I have never seen these before. They are shiny black, round and about 1/4 inch. Not baby bugs considering what they are doing (it doesn't look like a quilting bee).

My first thought was flea beetles but I have to admit, I've never seen a flea beetle but, they don't hop, they skitter and when really annoyed, fly.

From the description, I came up with white-margined burrower bug but, I live in the west and these bugs aren't eating mint seeds, they are sucking the life out of tomato fruits.

Luckily, they are only attacking 1 tomato plant in the middle of a whole row. I cut off the branch most of them were on and today, picked a couple more off tomato fruits. Anyone know what they might be?

For perspective, that is a 1 inch cherry tomato

Never seen those but probably don't have them way over here. From what I see, think they are beetles which would not have sucking parts, but I am not sure. Hope someone knows.
I would try to get rid of them though.

They are definitely sucking. I can see their tiny proboscises stuck into the tomato skins and they are ruining the tomatoes they attack. Luckily, they seem to be herd bugs so all crowd onto the same tomato fruit together. So far, I haven't had to get out the big guns (Pyrethrum). After cutting one whole branch off, I am picking just a couple off every day or so. Actually not picking, shaking. They don't hang on very well. They seem to be attracted to the ripest fruits so I'm also picking a little early. I just can't figure out where they're coming from as I'm only seeing adults.

Bugs, then. I don't have those but I have harlequin bugs, on brassicas, which I usually find as mature and paired adults, can't figure where all the juveniles hide but must be somewhere. Regardless, keep after those. Here we have small brown stinkbugs that like tomatoes.