find-and-split is a GitHub Action that finds and splits files:

- uses: remarkablemark/find-and-split@v1
  id: my-files
  with:
    pattern: '*.txt'
    chunk: 1/2

- name: Print files
  run: echo ${{ steps.my-files.outputs.files }}

It’s useful for test sharding, or splitting tests that can be run in parallel jobs. For example:

# .github/workflows/test.yml
name: test
on: push

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        shard: [1/2, 1/2]

    steps:
      - name: Checkout repository
        uses: actions/checkout@v4

      - name: Find and split files
        uses: remarkablemark/find-and-split@v1
        id: tests
        with:
          chunk: ${{ matrix.shard }}
          directory: tests
          pattern: '*Test.php'

      - name: Run tests
        run: |
          composer install
          vendor/bin/phpunit ${{ steps.tests.outputs.files }}

See the documentation and examples.