So I hate the default adventurer skins, even if it’s usually covered by armor and I use first-person camera. I have my own skin. But MineTest has no built-in config for skins! Mods to the rescue.
On your world select, hit Select Mods, Find More Mods, and search for skinsdb, and smart inventory, install both.
Back to menu, select each of those and Enable. Save.
Now in terminal:
cd ~/Library/Application Support/minetest/mods/skinsdb/textures cp ~/Pictures/My-Minecraft-Avatar.png character_whatever.png
This only seems to work with MC 1.0 avatars, even tho skinsdb says it works with MC 1.8; if you have multiple layers, remove those and resave without them. I tried installing the 3d_armor mod, which might enable that, and it has broken dependencies. 🙁
Play Game, and in game, open inventory, click the skin icon, and at the bottom of the big new Smart Inventory screen, skin icon. Select, done.
(The skin was originally a Spider Jerusalem skin, which I wanted a Nine Inch Nails shirt on, but there’s only room for NI, which makes it even better.)