You can probably build something over mix test --listen-on-stdin.

–listen-on-stdin - runs tests, and then listens on stdin. Receiving a newline will result in the tests being run again. Very useful when combined with --stale and external commands which produce output on stdout upon file system modification.

There is GitHub - lpil/mix-test.watch: 🎠 Because TDD is awesome · GitHub

Also https://medium.com/@andrew_dryga/run-stale-tests-on-file-change-in-elixir-6f8aac829973

Here’s two language-agnostic options I have used in the past:

entr:

git ls-files **/*.ex* | entr -cdp mix test [--stale]

watchexec

watchexec -c -p -e 'ex,exs,lock' -- mix test [--stale]

Here’s an Elixir-specific snippet from my dotfiles that I’m not sure of the provenance of, and that seems kind of overwrought, but I think it might have been derived from a José/Plataformatec tweet or something?

fswatch --latency=0.01 --one-per-batch lib/ test/ | MIX_ENV=test mix do test --stale, run --no-halt -e "IO.gets(:stdio, ''); IO.puts 'Restarting...'; :init.restart()"

And a variant for umbrella apps:

fswatch --latency=0.01 --one-per-batch apps/ config/ mix.exs mix.lock | MIX_ENV=test mix do test --stale, run --no-halt -e "IO.gets(:stdio, ''); IO.puts 'Restarting...'; :init.restart()"

Edit: I wasn’t entirely mistaken, this was a José gist that maybe got tweeted about: A 1LOC bash script for re-running tests whenever a lib/ or test/ file changes keeping the same VM instance · GitHub

Thanks! mix-test.watch works perfectly, including --stale support and clearing the screen before each test run.

I use Cortex myself:

Sweet. I’m actually back to the drawing board, because mix-test isn’t working for me in a Docker container with a Bind mount. I may need a tool that’s configureable enough to do polling.

This is really slick, thanks for sharing!

Anyone landing here using watchexec and experiencing it “hanging”, (you’ll see the beam process marked as T in htop), I had to add the --wrap-process=none flag.

eg:

watchexec --wrap-process=none -c -e ex,exs -- "mix test"

Since we’re necro-ing this thread, here’s what I use for my mix test watcher:

mix-test-watch

#!/bin/sh

until ag -g "\.(ex|exs|eex|heex)$" | entr -d sh -c 'mix test "$@"; echo ""; echo "Test run finished on: $(date -Iseconds)"' _ "$@"; do sleep 1; done

Requires ag (Silver Searcher, ripgrep version added below) and entr (which is also a useful tool for file watcher scripts):

Bonus: Ripgrep version (rg)

In honour of this thread, I have just upgraded it to work with rg (ripgrep):

mix-test-watch

#!/bin/sh

until rg --files -g "*.{ex,exs,eex,heex}" | entr -d sh -c 'mix test "$@"; echo ""; echo "Test run finished on: $(date -Iseconds)"' _ "$@"; do sleep 1; done

Misc. thoughts:

• This script must be run from the project root directory of whatever Elixir project you want to test. It should work with any Elixir package, since it’s just a file watcher that calls mix test.

• I added timestamps recently so that LLM agents could see the different timestamps as they work on their tasks (we both watch the test session via tmux).

• You can append custom args when calling the file, e.g. mix-test-watch test/some_file.ex --seed 0.

• Using entr is nice because you can manually trigger a run by pressing the spacebar key.

• There is a mix test watcher package which I will not name here, as prefer to use these common tools (ag/rg and entr) instead of adding another Hex dependency to each project.

Your necro is much appreciated, was looking for this exact info today.

Gravedigging is dirty work but someone’s got to do it.