Add development dependencies for PhpUnit.

Author: Potherca

composer.json

@@ -28,6 +28,11 @@
     "psr/http-factory": "^1.0",
     "psr/http-message": "^1.0"
   },
+  "require-dev": {
+    "ext-xdebug": "*",
+    "ext-xml": "*",
+    "phpunit/phpunit": "^9.5"
+  },
   "scripts": {
     "dev:example": "php -S localhost:${PORT:-8080} -t ./src/ ./src/example.php",
     "tests:unit": "phpunit --configuration `.config/phpunit.xml.dist` ./tests/unit"
@@ -36,8 +41,5 @@
     "dev:example": "Run internal PHP development server with example code",
     "tests:unit": "Run unit-test with PHPUnit"
   },
-  "type": "library",
-  "require-dev": {
-    "phpunit/phpunit": "^9"
-  }
+  "type": "library"
 }