Add mutation testing with Infection

.github/workflows/continuous-integration.yml

@@ -203,6 +203,22 @@ jobs:
       - name: Run phpstan
         run: vendor/bin/phpstan
 
+  mutation-testing:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Setup PHP
+        uses: shivammathur/setup-php@v2
+        with:
+          php-version: 8.4
+          extensions: intl, sodium, zip
+          tools: infection
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - uses: actions/checkout@v6
+      - uses: ramsey/composer-install@v3
+      - name: Run infection
+        run: sudo infection --min-msi=68 --min-covered-msi=68 --threads=4 --show-mutations=max --no-progress
+
   build-assets:
     needs:
       - unit-tests

infection.json5

@@ -0,0 +1,11 @@
+{
+    "$schema": "https://raw.githubusercontent.com/infection/infection/0.32.6/resources/schema.json",
+    "source": {
+        "directories": [
+            "src"
+        ]
+    },
+    "mutators": {
+        "@default": true
+    }
+}