Notifications: Add phpunit test for notification sending

Covers core case scenarios, and check of notification content.

app/Http/Controller.php

@@ -66,6 +66,16 @@ abstract class Controller extends BaseController
         }
     }
 
+    /**
+     * Prevent access for guest users beyond this point.
+     */
+    protected function preventGuestAccess(): void
+    {
+        if (!signedInUser()) {
+            $this->showPermissionError();
+        }
+    }
+
     /**
      * Check the current user's permissions against an ownable item otherwise throw an exception.
      */