Refactor test_sync_hub_node_backfill: streamline imports and utilize shared DB helpers

.github/skills/code-standards/SKILL.md

@@ -74,6 +74,18 @@ Use sanitizers from `server/helper.py` before storing user input. MAC addresses
 - Everything is already writable
 - If permissions needed, fix `.devcontainer/scripts/setup.sh`
 
+## Test Helpers — No Duplicate Mocks
+
+Reuse shared mocks and factories from `test/db_test_helpers.py`. Never redefine `DummyDB`, `make_db`, or inline DDL in individual test files.
+
+```python
+import sys, os
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+from db_test_helpers import make_db, DummyDB, insert_device, minutes_ago
+```
+
+If a helper you need doesn't exist yet, add it to `db_test_helpers.py` — not locally in the test file.
+
 ## Path Hygiene
 
 - Use environment variables for runtime paths

test/scan/test_sync_hub_node_backfill.py

@@ -1,37 +1,19 @@
 """Tests for update_sync_hub_node backfill."""
 
-import sqlite3
+import sys
+import os
 from unittest.mock import patch
 
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))
+from db_test_helpers import make_db, DummyDB  # noqa: E402
+
 from server.scan import device_handling
 
 
-class DummyDB:
-    """Minimal DB wrapper compatible with device_handling helpers."""
-
-    def __init__(self, conn):
-        self.sql = conn.cursor()
-        self._conn = conn
-
-    def commitDB(self):
-        self._conn.commit()
-
-
 def _make_db(devices):
-    """Create an in-memory DB with a Devices table and seed rows."""
-    conn = sqlite3.connect(":memory:")
-    conn.row_factory = sqlite3.Row
+    """Create an in-memory DB with full schema and seed rows."""
+    conn = make_db()
     cur = conn.cursor()
-
-    cur.execute(
-        """
-        CREATE TABLE Devices (
-            devMac TEXT PRIMARY KEY,
-            devSyncHubNode TEXT
-        )
-        """
-    )
-
     cur.executemany(
         "INSERT INTO Devices (devMac, devSyncHubNode) VALUES (?, ?)",
         devices,