Getting Started with Github Actions.md

Getting Started with Github Actions

The High Level

Github Actions is a system for running workflows on Github's infrastructure to "do stuff when things happen". More specifically:

• Your Github Actions workflows live in the .github/workflows directory in your repository.
• Github Actions will trigger when an event happens and kick off a workflow that consists of one or more jobs.

A First Workflow

Let's take a look at a very simple workflow that will run our unit tests.

name: Unit Tests

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  build-and-test:
    runs-on: ubuntu-latest

    steps:
      - uses: actions/checkout@v3
      - name: Setup Node
        uses: actions/setup-node@v3
      - run: npm ci
      - run: npm test

Okay, so what's going on here:

• name: Signifies the name of the worklow, which you can see in the screenshot.
• on: What kind of event are we listening for? In this case, we're listening for two events:
  • A push to the main branch.
  • A pull_request that targets the main branch.
• jobs: A list of jobs that will run in parallel. Right now, we only have one and it's called build-and-test.
• steps each job has one or more steps. These steps run synchronously (one after the other). Right now, we have the following steps:
  • actions/checkout@v3: This one is super important. It checks out the repository. For most actions where you might want to run tests, build your application, deploy your application, etc., you're probably going to need the repository, right?
  • actions/setup-node@v3: We gave this one the cute name "Setup Node" as well. But, this one does what it says on the tin. It installs Node.js onto whatever container your action is running in.
  • run: I'll get into this in a bit, but really, you have two major types of things you can do: run commands and use actions. In this case, we're running npm ci and then npm test.

Whoa, What is npm ci?

npm ci is a variation on npm install, but it has a few important cavaets:

• It insists on you already having a package-lock.json.
• It will error out instead of updating package-lock.json if something doesn't match.
• It install all of the dependencies. I.e. you can't just use it to install one depenedency like npm ci @testing-library/react or something.
• It blows away node_modules if present.
• It doesn't write to package.json.

Experiments

• Right now build-and-test only tests. Maybe it should build first?
• Could you add a name to the step where we check out the repository? What would that look like?
• Challenge Mode: What if wanted to run npm run build in parallel with npm test?