phpunit test must be installed in www/ folder

Because www folder is source base, if phpunit is installed outside it
cannot find the classes

www/composer.json

@@ -13,5 +13,8 @@
         "classmap": [
             "lib/"
         ]
+    },
+    "require-dev": {
+        "phpunit/phpunit": "^9"
     }
 }