GitHub Actions: build & test (no push)

name: build-and-test
on:
  pull_request:

permissions:
  contents: read

jobs:
  build:
    runs-on: ubuntu-latest
    timeout-minutes: 15
    steps:
      - uses: actions/checkout@v4

      - uses: docker/setup-buildx-action@v3

      - name: Build the image (load it, don't push it)
        uses: docker/build-push-action@v6
        with:
          # docker/setup-buildx-action creates a docker-container builder,
          # which -- unlike the daemon's own default builder -- keeps a
          # build's result in its own cache instead of the local image
          # store. Without load: true here, the next step's "docker run"
          # fails with "Unable to find image" even though the build
          # itself succeeded.
          load: true
          tags: app:ci
          cache-from: type=gha
          cache-to: type=gha,mode=max

      - name: Run the test suite inside the built image
        run: docker run --rm app:ci npm test