Add mutation testing to pipeline

Author: marijnvanwezel

.github/workflows/main.yml

@@ -41,6 +41,11 @@ jobs:
           rm -f installer expected
           mv composer.phar /usr/local/bin/composer
 
+      - name: Install Xdebug
+        run: |
+          pecl install xdebug
+          docker-php-ext-enable xdebug
+
       - name: Checkout repository
         uses: actions/checkout@v2
         with:
@@ -51,4 +56,7 @@ jobs:
         run: composer update --working-dir ${{ env.INSTALL_PATH }}
 
       - name: Run unit tests
-        run: composer test --working-dir ${{ env.INSTALL_PATH }}
+        run: composer test --working-dir ${{ env.INSTALL_PATH }}
+
+      - name: Run mutation tests
+        run: composer infect --working-dir ${{ env.INSTALL_PATH }}

composer.json

@@ -39,7 +39,8 @@
     "ext-ctype": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "~9.0"
+    "phpunit/phpunit": "~9.0",
+    "infection/infection": "^0.25.5"
   },
   "autoload": {
     "psr-4": {
@@ -52,7 +53,8 @@
     }
   },
   "scripts": {
-    "test": "phpunit tests/"
+    "test": "phpunit tests/",
+    "infect": "XDEBUG_MODE=coverage infection --show-mutations"
   },
   "minimum-stability": "stable",
   "prefer-stable": true

infection.json

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