Updated and added tests for new default user system

Closes #138

app/Http/Controllers/UserController.php

@@ -187,7 +187,7 @@ class UserController extends Controller
 
     /**
      * Show the user delete page.
-     * @param $id
+     * @param int $id
      * @return \Illuminate\View\View
      */
     public function delete($id)
@@ -220,6 +220,11 @@ class UserController extends Controller
             return redirect($user->getEditUrl());
         }
 
+        if ($user->system_name === 'public') {
+            session()->flash('error', 'You cannot delete the guest user');
+            return redirect($user->getEditUrl());
+        }
+
         $this->userRepo->destroy($user);
         session()->flash('success', 'User successfully removed');