What are composite actions in GitHub Actions? How do you create a custom action?

my-actions/
└── setup-and-test/
    └── action.yml     ← the composite action

# .github/actions/setup-and-test/action.yml
name: 'Setup Java and Run Tests'
description: 'Sets up JDK, caches Maven, and runs TestNG suite'

inputs:
  java-version:
    description: 'Java version to use'
    required: false
    default: '17'
  browser:
    description: 'Browser for tests'
    required: false
    default: 'chrome'
  suite:
    description: 'TestNG suite file'
    required: false
    default: 'testng.xml'
  environment:
    description: 'Target environment'
    required: true

outputs:
  test-status:
    description: 'Pass or Fail'
    value: ${{ steps.run-tests.outcome }}

runs:
  using: 'composite'      # ← makes this a composite action
  steps:
    - name: Set up JDK
      uses: actions/setup-java@v4
      with:
        java-version: ${{ inputs.java-version }}
        distribution: temurin
        cache: maven

    - name: Install Chrome
      shell: bash
      run: |
        sudo apt-get update -q
        sudo apt-get install -y google-chrome-stable

    - name: Run tests
      id: run-tests
      shell: bash
      run: |
        mvn test \
          -Dbrowser=${{ inputs.browser }} \
          -Denv=${{ inputs.environment }} \
          -Dsurefire.suiteXmlFiles=${{ inputs.suite }}

    - name: Upload results
      if: always()
      uses: actions/upload-artifact@v4
      with:
        name: results-${{ inputs.environment }}-${{ inputs.browser }}
        path: target/surefire-reports/

# .github/workflows/ci.yml
name: CI

on: [push, pull_request]

jobs:
  smoke-test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Setup and run smoke tests
        uses: ./.github/actions/setup-and-test    # local path
        # OR from another repo:
        # uses: my-org/shared-actions/setup-and-test@v1
        with:
          browser:     chrome
          suite:       smoke-testng.xml
          environment: staging

  regression-firefox:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Setup and run regression on Firefox
        uses: ./.github/actions/setup-and-test
        with:
          browser:     firefox
          suite:       regression-testng.xml
          environment: qa

# action.yml (at repo ROOT for marketplace publishing)
name: 'Run Selenium Tests'
description: 'Run Selenium/TestNG automation tests with configurable browser and environment'
author: 'AutomateQA'

branding:
  icon:  'play-circle'
  color: 'green'

inputs:
  browser:
    description: 'Browser (chrome/firefox/edge)'
    required: false
    default: 'chrome'

runs:
  using: 'composite'
  steps:
    - shell: bash
      run: echo "Running tests on ${{ inputs.browser }}"