github_actions_demo.md

Demo: Automation with GitHub Actions

1. Setting up a Test Job

• Clone automation lecture repository and run code and tests

• Set up workflow file

  mkdir -p .github/workflows
  cd .github/workflows
  vi testing.yml

• In the first go, we only want to run the unittest tests.

• Edit testing.yml to have following content

  name: Testing workflow
  
  on: [push, pull_request]
  
  jobs:
    test:
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v6
        - uses: actions/setup-python@v6
          with:
            python-version: '3.10'
        - name: "Run unittest"
          run: python -m unittest

• runs-on does not refer to a Docker container, but to a runner tag.

• This specific Python version as it is the current version on my laptop (and let's say I want to reproduce this environment)

• Add, commit, push

• After the push, inspect "Action" panel on GitHub repository

  • GitHub will schedule a run (yellow dot)
  • Hooray. We have set up our first action.

• Failing test example:

  • Edit settings on GitHub that one can only merge if all tests pass:
    • Settings -> Branches -> Branch protection rule
    • Choose main branch
    • Enable "Require status checks to pass before merging". Optionally enable "Require branches to be up to date before merging"
    • Choose status checks that need to pass: test
    • Click on "Create" at bottom of page.
  • Create a new branch break-code.
  • Edit operations.py, break the code, commit it and push it to the branch. Afterwards open a new PR and inspect the failing test. We are also not able to merge the changes as the "Merge" button should be inactive.

2. Extend Action to Have Several Dependent Jobs

• Briefly explain what black is: a compact, easy-to-use formatting tool.

  • Run black locally on repository and explain what it does.

    black --check .

  • Add an empty line somewhere and run again.

  • Run without --check and git status.

• Adding additional jobs by editing on GitHub. The workflow should have the following content:

  name: Testing workflow
  
  on: [push, pull_request]
  
  jobs:
    style:
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v6
        - uses: actions/setup-python@v6
          with:
            python-version: '3.10'
        - name: "Install style checker"
          run: pip install black
        - name: "Run style check"
          run: black --check .
    build:
      needs: style
      runs-on: ubuntu-latest
      env:
        PROJECT_NAME: "Automation Lecture"
      steps:
        - name: "Run build phase"
          run: echo "Building project $PROJECT_NAME"
    test:
      # needs: build
      runs-on: ubuntu-latest
      steps:
        - uses: actions/checkout@v6
        - uses: actions/setup-python@v6
          with:
            python-version: '3.10'
        - name: "Run unittest"
          run: python -m unittest

• We need to run actions/checkout in each job

  • We could share the repository between jobs via artifacts, but that is uncommon.

• We need to run actions/setup-python since jobs do not share the environment.

• We specify dependencies by needs such that the steps run after each other.

• We do not have a real build step since it is Python. However, this might be interesting for compiled code.

3. Other Workflows

• Show workflows of preCICE
  • Show Actions tab
    • Build and test job, click on a run
    • Jobs created through test matrix
    • Click on a job, click on a few steps
  • Show workflows folder, click on Build and Test
  • Only one job. build, test, ... are modeled as steps

4. act Demo

• act is for quick checks while developing workflows, not for developing the code

• Check available jobs

  act -l

• Run jobs for push event (default event)

  act

• Run a specific job

  act -j test