A 1LOC bash script for re-running tests whenever a lib/ or test/ file changes keeping the same VM instance

watcher.sh

# You will need fswatch installed (available in homebrew and friends)
# The command below will run tests and wait until fswatch writes something.
# The --stale flag will only run stale entries, it requires Elixir v1.3.
fswatch lib/ test/ | mix test --stale --listen-on-stdin

You probably want the --one-per-batch flag, and perhaps also --latency=0.01 or similar to make it more snappy. These are for fswatch, as you might have guess, but just to be crystal clear.

--listen-on-stdin doesn't seem to be supported, my take on this:

fswatch -0 --latency=0.01 --one-per-batch lib test web  | xargs -0 -n 1 mix test --stale test/