A GitHub action to report code coverage

ci.yaml

name: ci

on:
  pull_request:
    branches: [ main ]

jobs:
  test:
    runs-on: ubuntu-latest
    env:
      WORKING_DIRECTORY: backend/cloud_functions
    steps:
      - uses: actions/checkout@v2

      - name: Install dependencies
        working-directory: ${{ env.WORKING_DIRECTORY }}
        run: npm install

      # Running tests for head branch and create a coverage report.
      - name: Run tests
        working-directory: ${{ env.WORKING_DIRECTORY }}
        run: |
          npm install -g nyc
          npm run ci

      # In order to show the coverage difference between head and base branch,
      # we need to create a coverage report for the base branch as well.
      - name: Create coverage report for base branch
        run: |
          mv $WORKING_DIRECTORY/coverage/lcov.info $WORKING_DIRECTORY/coverage/lcov_head.info
          git fetch
          git checkout origin/${{ github.event.pull_request.base.ref }}
          cd $WORKING_DIRECTORY && npm run ci

      - name: Post coverage report
        uses: romeovs/lcov-reporter-action@v0.3.1
        with:
          lcov-file: "${{ env.WORKING_DIRECTORY }}/coverage/lcov_head.info"
          lcov-base: "${{ env.WORKING_DIRECTORY }}/coverage/lcov.info"
          github-token: "${{ secrets.GITHUB_TOKEN }}"
          delete-old-comments: true