SIENTIAPDE-1205

Enhance unit tests for async shutdown and improve assertions

- Updated `test_app.py` to verify multiple calls to `asyncio_sleep` and ensure proper handling of sleep intervals.
- Added new tests in `test_ingestor.py` and `test_opc_manager.py` to validate shutdown behavior and error handling for async operations.
- Improved assertions in existing tests to enhance reliability and clarity of test outcomes.

tests/unit/test_ingestor.py

@@ -82,6 +82,13 @@ def ingestor_manager_started(ingestor):
     return ingestor
 
 
+@mark.asyncio
+async def test_shutdown(ingestor_manager_started):
+    await ingestor_manager_started.shutdown()
+
+    ingestor_manager_started.ingestor_manager.shutdown.assert_called_once()
+
+
 @mark.asyncio
 async def test_handle_acquired_tags_not_acquired(ingestor_manager_started):
     await ingestor_manager_started.handle_acquired_tags([])