Use watchexec to automatically run your Elixir code checks


Alan Vardy
 cli  elixir  tests

Gears From Unsplash

What is it

watchexec is a command line tool that executes commands whenever changes happen in a given directory.

Why use it

It’s pretty common to bounce between making small code changes and running mix test, instead of manually toggling between two windows our workflow can be dramatically increased by just having the tests run again every time a file is saved.

A simple example

Run mix test every time a file with an extension ex or exs is modified.

watchexec -e ex,exs "mix test"

Lint with Credo as well

We can take it a step further and only run the tests if Credo static analysis has passed.

watchexec -e ex,exs "mix credo && mix test"

Show failing tests one at a time

If we have a lot of failing tests we can run them one at a time. Setting the seed manually ensures that they are run in the same order with the same parameters - this is helpful when debugging!

watchexec -e ex,exs "mix test --failed --seed 9 --max-failures 1 && mix test --max-failures 1 --seed 9"

We are limited only by imagination

If we are using a large monitor it’s relatively easy to set up a couple of different terminals automatically running our tests for us on every iteration and allowing us to keep our cursors in the code where they belong.

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