This article is outdated as of 2020/05/05 because it refers to the previous implementation of GitHub Actions. I’ve put together a newer version at Using GitHub Actions to Test Racket Code (Revsied) so you probably want to read that instead.
Like Alex Harsányi, I’ve been looking for a good, free-as-in-beer, alternative to Travis CI. For now, I’ve settled on GitHub Actions because using them is straightforward and because I saves me from creating yet another account with some other company.
GitHub Actions revolves around the concept of “workflows” and “actions”. Actions execute arbitrary Docker containers on top of a checked-out repository and workflows describe which actions need to be executed when a particular event occurs. During the execution of a workflow, all actions, including ones running in parallel, share the same physical workspace. All of this stuff is declaratively specified using HCL.
Here’s an example workflow:
This is saying that there is a workflow called “demo” that is executed
whenever anything is pushed to the repository. That workflow’s goal
is to execute the “echo” action, which happens to depend on actions
“make-a” and “make-b”. When the workflow is triggered, those two
actions are run first and the “echo” action only runs after they both
succeed. In this particular example, each of the actions runs a shell
command on top of the
alpine docker image, but I could’ve picked any
other image from Docker Hub or any existing GitHub Action repository.
This page describes all of the various workflow configuration
If you save the above config in a file called
in any GitHub repository and visit the “Actions” tab, then – assuming
you have access to the GitHub Actions beta – you should see the
pipeline execute almost immediately and output:
We can leverage all of this to test a Racket package is by using Jack Firth’s racket image (or you could roll your own and host it on Docker Hub yourself):
Here are the contents of
The script sets the working directory to
testpackage's (a hypothetical package for the purposes of
this article) dependencies and then runs its tests.
That’s all there is to it! With about 12 LOC we’ve put together a basic workflow that tests a package on every commit.
Gotchas & Limitations
Like I mentioned before, all actions in a workflow share the same workspace so it’s possible for actions to clash with one another when they operate on the filesystem. That’s something you have to keep in mind when designing your workflows.
Workflow and action names share a namespace. If you call your workflow “test” and your action “test”, you’ll get an error saying the workflow is invalid, but it won’t point out exactly why.
Finally, there’s no built-in support for notifications. When builds
fail, you won’t notice unless you visit the Actions tab. For one of
my non-OSS projects, I’ve set up a Telegram bot that I can use to
notify a particular channel whenever builds succeed or fail. That
works, but it’s fairly ugly because there doesn’t seem to be any way
to conditionally execute actions (i.e. things like “if action
fails then run action
b”), so I had to bundle the
notification-handling code into each of my action scripts.