Require phpunit/php-code-coverage

Author: ruudk

composer.json

@@ -27,6 +27,7 @@
   },
   "require-dev": {
     "guzzlehttp/promises": "^1.5.0 || ^2.0.0",
+    "phpunit/php-code-coverage": "^9.2.27",
     "phpunit/phpunit": "^9.6.11",
     "react/promise": "^2.8.0",
     "webonyx/graphql-php": "^14.0"