test(09-01): add failing tests for retention cleanup service

- Test cleanup deletes expired snapshots
- Test snapshots within retention window are kept
- Test deleted count is returned
- Test empty table handled gracefully

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/tests/test_retention_service.py

@@ -0,0 +1,128 @@
+"""Tests for retention cleanup service.
+
+Tests the cleanup_expired_snapshots function with mocked AdminAsyncSessionLocal
+and mocked settings.CONFIG_RETENTION_DAYS.
+"""
+
+import pytest
+from unittest.mock import AsyncMock, MagicMock, patch
+
+
+@pytest.mark.asyncio
+async def test_cleanup_deletes_expired_snapshots():
+    """Test 1: cleanup_expired_snapshots deletes snapshots with collected_at older than retention_days."""
+    from app.services.retention_service import cleanup_expired_snapshots
+
+    mock_session = AsyncMock()
+    mock_result = MagicMock()
+    mock_result.rowcount = 5
+    mock_session.execute = AsyncMock(return_value=mock_result)
+    mock_session.commit = AsyncMock()
+
+    mock_ctx = AsyncMock()
+    mock_ctx.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_ctx.__aexit__ = AsyncMock(return_value=False)
+
+    with patch(
+        "app.services.retention_service.AdminAsyncSessionLocal",
+        return_value=mock_ctx,
+    ), patch(
+        "app.services.retention_service.settings",
+    ) as mock_settings:
+        mock_settings.CONFIG_RETENTION_DAYS = 90
+        count = await cleanup_expired_snapshots()
+
+    # Should execute the DELETE query
+    mock_session.execute.assert_called_once()
+    # Verify DELETE uses make_interval with the configured days
+    sql_text = str(mock_session.execute.call_args[0][0].text)
+    assert "make_interval" in sql_text
+    assert "DELETE" in sql_text
+    assert "router_config_snapshots" in sql_text
+    # Should commit
+    mock_session.commit.assert_called_once()
+    # Should return the deleted count
+    assert count == 5
+
+
+@pytest.mark.asyncio
+async def test_cleanup_keeps_snapshots_within_retention_window():
+    """Test 2: cleanup_expired_snapshots keeps snapshots within the retention window."""
+    from app.services.retention_service import cleanup_expired_snapshots
+
+    mock_session = AsyncMock()
+    mock_result = MagicMock()
+    mock_result.rowcount = 0  # No rows deleted means all within window
+    mock_session.execute = AsyncMock(return_value=mock_result)
+    mock_session.commit = AsyncMock()
+
+    mock_ctx = AsyncMock()
+    mock_ctx.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_ctx.__aexit__ = AsyncMock(return_value=False)
+
+    with patch(
+        "app.services.retention_service.AdminAsyncSessionLocal",
+        return_value=mock_ctx,
+    ), patch(
+        "app.services.retention_service.settings",
+    ) as mock_settings:
+        mock_settings.CONFIG_RETENTION_DAYS = 90
+        count = await cleanup_expired_snapshots()
+
+    assert count == 0
+
+
+@pytest.mark.asyncio
+async def test_cleanup_returns_deleted_count():
+    """Test 3: cleanup_expired_snapshots returns count of deleted rows."""
+    from app.services.retention_service import cleanup_expired_snapshots
+
+    mock_session = AsyncMock()
+    mock_result = MagicMock()
+    mock_result.rowcount = 42
+    mock_session.execute = AsyncMock(return_value=mock_result)
+    mock_session.commit = AsyncMock()
+
+    mock_ctx = AsyncMock()
+    mock_ctx.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_ctx.__aexit__ = AsyncMock(return_value=False)
+
+    with patch(
+        "app.services.retention_service.AdminAsyncSessionLocal",
+        return_value=mock_ctx,
+    ), patch(
+        "app.services.retention_service.settings",
+    ) as mock_settings:
+        mock_settings.CONFIG_RETENTION_DAYS = 30
+        count = await cleanup_expired_snapshots()
+
+    assert count == 42
+
+
+@pytest.mark.asyncio
+async def test_cleanup_handles_empty_table():
+    """Test 4: cleanup_expired_snapshots handles empty table (returns 0)."""
+    from app.services.retention_service import cleanup_expired_snapshots
+
+    mock_session = AsyncMock()
+    mock_result = MagicMock()
+    mock_result.rowcount = 0
+    mock_session.execute = AsyncMock(return_value=mock_result)
+    mock_session.commit = AsyncMock()
+
+    mock_ctx = AsyncMock()
+    mock_ctx.__aenter__ = AsyncMock(return_value=mock_session)
+    mock_ctx.__aexit__ = AsyncMock(return_value=False)
+
+    with patch(
+        "app.services.retention_service.AdminAsyncSessionLocal",
+        return_value=mock_ctx,
+    ), patch(
+        "app.services.retention_service.settings",
+    ) as mock_settings:
+        mock_settings.CONFIG_RETENTION_DAYS = 90
+        count = await cleanup_expired_snapshots()
+
+    assert count == 0
+    mock_session.execute.assert_called_once()
+    mock_session.commit.assert_called_once()