Add Infection mutation testing as a CI signal

.github/workflows/mutation.yml

@@ -0,0 +1,45 @@
+name: Mutation Testing
+
+on:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: mutation-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  mutation:
+    name: Infection
+    runs-on: ubuntu-latest
+    timeout-minutes: 15
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Setup PHP with PCOV
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: '8.4'
+          extensions: mbstring, xml, curl, intl, json, mysqlnd, sockets
+          coverage: pcov
+
+      - name: Install Composer dependencies
+        run: composer install --prefer-dist --no-progress --no-interaction
+
+      - name: Run Infection
+        run: composer infection -- --no-interaction
+
+      - name: Upload Infection report
+        if: always() && !cancelled()
+        uses: actions/upload-artifact@v4
+        with:
+          name: infection-report
+          path: |
+            build/logs/infection.html
+            build/logs/infection.json
+          if-no-files-found: warn
+          retention-days: 14

composer.json

@@ -21,6 +21,7 @@
     },
     "require-dev": {
         "fakerphp/faker": "^1.9",
+        "infection/infection": "^0.35.4",
         "mikey179/vfsstream": "^1.6",
         "phpunit/phpunit": "^13.0"
     },
@@ -42,7 +43,10 @@
     "config": {
         "optimize-autoloader": true,
         "preferred-install": "dist",
-        "sort-packages": true
+        "sort-packages": true,
+        "allow-plugins": {
+            "infection/extension-installer": true
+        }
     },
     "scripts": {
         "test": "phpunit --testsuite UnitFeature --exclude-group integration,integration-websocket",
@@ -54,6 +58,7 @@
         "test:all": "phpunit --exclude-group integration-websocket",
         "test:coverage": "phpunit --colors --coverage-html build/logs/html",
         "test:coverage:text": "phpunit --colors --coverage-text",
+        "infection": "@php -d memory_limit=1G vendor/bin/infection --threads=4 --show-mutations",
         "analyse": "phpstan analyse --memory-limit=256M",
         "cs-check": "php-cs-fixer fix --dry-run --diff",
         "cs-fix": "php-cs-fixer fix"