test: add more assertions to AsyncMultiRangeDownloader creation test

Author: zhixiangli

packages/google-cloud-storage/tests/unit/asyncio/test_async_multi_range_downloader.py

@@ -431,6 +431,8 @@ async def test_create_mrd_with_generation_number(
 
         # Assert
         assert mrd.generation == _TEST_GENERATION_NUMBER
+        assert mrd.read_handle == _TEST_READ_HANDLE
+        assert mrd.persisted_size == _TEST_OBJECT_SIZE
         assert "'generation_number' is deprecated" in caplog.text
 
     @pytest.mark.asyncio