tests: ensure get_cached_fetcher reuses instance in threaded test

Author: rodrigo.nogueira

tests/test_readme_examples.py

@@ -21,6 +21,10 @@ async def fetch_data(key: str) -> str:
 
     async def worker() -> tuple[str, Any]:
         fetcher = get_cached_fetcher()
+        # Call again to ensure the pattern handles the "already exists" case
+        fetcher_retry = get_cached_fetcher()
+        assert fetcher is fetcher_retry
+
         result = await fetcher("some_key")
         return result, fetcher.cache_info()