See https://adventofcode.com/.
I'm using Advent of Code 2022 as an opportunity to learn Elixir. Elixir was recommended to me by Xavier, who gave us at Cryptosense a presentation about it a while ago.
This is now set up as a Mix library project. To run everything, just say mix.
Tests now run automatically in CI on every push; see workflow defined in
elixir.yml.
There's even a pretty CI status badge at the top of this page!