Add custom "test" composer command

Like NPM, just run `composer run test`

Author: pH-7

composer.json

@@ -31,5 +31,8 @@
   },
   "require-dev": {
     "phpunit/phpunit": "^9.5"
+  },
+  "scripts": {
+    "test": "vendor/bin/phpunit"
   }
 }