Testing wise, elixir is fantastic. I have a relatively large codebase where I run what are effectively full on simulations of the system in sharded-by-test partitions of state to verify correctness and robustness of the code. There are about 60 of those that run concurrently with the unit tests and the whole thing closes in 10 seconds.

Docs for elixir are pretty, too: here's a library that I wrote. The doc system is extensible enough that I could patch in docstrings from another language and also hyperlink (the </> buttons link to github) the GitHub code across languages (the `zig structs` section in the sidebar is autogenerated by parsing zig code) https://hexdocs.pm/zigler/Zigler.html

My joke is that you want to write documentation that's pretty and html-responsive enough that you can read it on the can between coding sprints.