add test

app/Http/Resources/ToDoResource.php

@@ -19,7 +19,7 @@ class ToDoResource extends JsonResource
             'user_id' => $this->user_id,
             'name' => $this->name,
             'description' => $this->description,
-            'checked' => $this->checked,
+            'checked' => $this->checked?->format('Y-m-d H:i:s'),
             'duration' => $this->duration,
         ];
     }