Document task DB access and unify background task DB handling

backend/tests/test_tasks/test_task_db.py

@@ -0,0 +1,44 @@
+"""Tests for the shared background task database helper."""
+
+from __future__ import annotations
+
+from unittest.mock import AsyncMock, patch
+
+import pytest
+
+from app.tasks.db import task_db
+
+
+class FakeSettings:
+    database_path = "/tmp/fake.db"
+
+
+@pytest.mark.asyncio
+async def test_task_db_opens_and_closes_connection() -> None:
+    """``task_db`` must open a DB connection and close it after use."""
+    fake_db = AsyncMock()
+    fake_db.close = AsyncMock()
+
+    with patch("app.tasks.db.open_db", new_callable=AsyncMock, return_value=fake_db) as mock_open_db:
+        async with task_db(FakeSettings()) as db:
+            assert db is fake_db
+
+    mock_open_db.assert_awaited_once_with("/tmp/fake.db")
+    fake_db.close.assert_awaited_once()
+
+
+@pytest.mark.asyncio
+async def test_task_db_closes_connection_on_exception() -> None:
+    """``task_db`` must close the connection even when the body raises."""
+    fake_db = AsyncMock()
+    fake_db.close = AsyncMock()
+
+    with patch(
+        "app.tasks.db.open_db",
+        new_callable=AsyncMock,
+        return_value=fake_db,
+    ), pytest.raises(RuntimeError, match="boom"):
+        async with task_db(FakeSettings()):
+            raise RuntimeError("boom")
+
+    fake_db.close.assert_awaited_once()