♻️(backend) extract notify_participant to util function

Move from lobby service to utils for reuse across services. Method is
generic enough for utility status. Future: create dedicated LiveKit
service to encapsulate all LiveKit-related utilities.

src/backend/core/tests/test_utils.py

@@ -2,9 +2,13 @@
 Test utils functions
 """
 
+import json
 from unittest import mock
 
-from core.utils import create_livekit_client
+import pytest
+from livekit.api import TwirpError
+
+from core.utils import NotificationError, create_livekit_client, notify_participants
 
 
 @mock.patch("asyncio.get_running_loop")
@@ -60,3 +64,105 @@ def test_create_livekit_client_custom_configuration(
     create_livekit_client(custom_configuration)
 
     mock_livekit_api.assert_called_once_with(**custom_configuration, session=None)
+
+
+@mock.patch("core.utils.create_livekit_client")
+def test_notify_participants_error(mock_create_livekit_client):
+    """Test participant notification with API error."""
+
+    # Set up the mock LiveKitAPI and its behavior
+    mock_api_instance = mock.Mock()
+    mock_api_instance.room = mock.Mock()
+    mock_api_instance.room.send_data = mock.AsyncMock(
+        side_effect=TwirpError(msg="test error", code=123, status=123)
+    )
+
+    class MockResponse:
+        """LiveKit API response mock with non-empty rooms list."""
+
+        rooms = ["room-1"]
+
+    mock_api_instance.room.list_rooms = mock.AsyncMock(return_value=MockResponse())
+
+    mock_api_instance.aclose = mock.AsyncMock()
+    mock_create_livekit_client.return_value = mock_api_instance
+
+    # Call the function and expect an exception
+    with pytest.raises(NotificationError, match="Failed to notify room participants"):
+        notify_participants(room_name="room-number-1", notification_data={"foo": "foo"})
+
+    # Verify that the service checked for existing rooms
+    mock_api_instance.room.list_rooms.assert_called_once()
+
+    # Verify send_data was called
+    mock_api_instance.room.send_data.assert_called_once()
+
+    # Verify aclose was still called after the exception
+    mock_api_instance.aclose.assert_called_once()
+
+
+@mock.patch("core.utils.create_livekit_client")
+def test_notify_participants_success_no_room(mock_create_livekit_client):
+    """Test the notify_participants function when the LiveKit room doesn't exist."""
+
+    # Set up the mock LiveKitAPI and its behavior
+    mock_api_instance = mock.Mock()
+    mock_api_instance.room = mock.Mock()
+    mock_api_instance.room.send_data = mock.AsyncMock()
+
+    # Create a proper response object with an empty rooms list
+    class MockResponse:
+        """LiveKit API response mock with empty rooms list."""
+
+        rooms = []
+
+    mock_api_instance.room.list_rooms = mock.AsyncMock(return_value=MockResponse())
+    mock_api_instance.aclose = mock.AsyncMock()
+    mock_create_livekit_client.return_value = mock_api_instance
+
+    notify_participants(room_name="room-number-1", notification_data={"foo": "foo"})
+
+    # Verify that the service checked for existing rooms
+    mock_api_instance.room.list_rooms.assert_called_once()
+
+    # Verify the send_data method was not called since no room exists
+    mock_api_instance.room.send_data.assert_not_called()
+
+    # Verify the connection was properly closed
+    mock_api_instance.aclose.assert_called_once()
+
+
+@mock.patch("core.utils.create_livekit_client")
+def test_notify_participants_success(mock_create_livekit_client):
+    """Test successful participant notification."""
+
+    # Set up the mock LiveKitAPI and its behavior
+    mock_api_instance = mock.Mock()
+    mock_api_instance.room = mock.Mock()
+    mock_api_instance.room.send_data = mock.AsyncMock()
+
+    class MockResponse:
+        """LiveKit API response mock with non-empty rooms list."""
+
+        rooms = ["room-1"]
+
+    mock_api_instance.room.list_rooms = mock.AsyncMock(return_value=MockResponse())
+
+    mock_api_instance.aclose = mock.AsyncMock()
+    mock_create_livekit_client.return_value = mock_api_instance
+
+    # Call the function
+    notify_participants(room_name="room-number-1", notification_data={"foo": "foo"})
+
+    # Verify that the service checked for existing rooms
+    mock_api_instance.room.list_rooms.assert_called_once()
+
+    # Verify the send_data method was called
+    mock_api_instance.room.send_data.assert_called_once()
+    send_data_request = mock_api_instance.room.send_data.call_args[0][0]
+    assert send_data_request.room == "room-number-1"
+    assert json.loads(send_data_request.data.decode("utf-8")) == {"foo": "foo"}
+    assert send_data_request.kind == 0  # RELIABLE mode in Livekit protocol
+
+    # Verify aclose was called
+    mock_api_instance.aclose.assert_called_once()