test: P2测试覆盖 — user/pool/schema_drift端点 43个新测试 (895→1017全通过)

新增测试文件:
- test_user_endpoint.py (18 tests): 用户CRUD/列表过滤/权限控制/自删保护
- test_pool_endpoint.py (12 tests): 连接池状态/重置/概览/mock外部依赖
- test_schema_drift_endpoint.py (13 tests): Schema快照捕获/漂移检测/历史查询

覆盖率提升:
- user端点: 0→18 tests (CRUD+权限+重复用户名+自删保护)
- pool端点: 0→12 tests (stats/reset/overview+角色访问控制)
- schema_drift端点: 0→13 tests (capture/check/history+dict序列化兼容)

修复: run.sh启动脚本同步

backend/tests/test_instance_permission.py

@@ -9,8 +9,11 @@
 - 集成测试: query/ticket 端点权限检查
 """
 import json
+import sys
 import pytest
+from contextlib import asynccontextmanager
 from fastapi import HTTPException
+from unittest.mock import patch, AsyncMock, MagicMock
 
 from app.models.instance import Instance
 from app.models.instance_group import InstanceGroup, user_groups
@@ -243,7 +246,7 @@ class TestPermissionEndpointIntegration:
     async def test_query_with_permission(
         self, client, db, developer_user, group_with_permissions
     ):
-        """有 query:select 权限 → 查询不被 403"""
+        """有 query:select 权限 → 查询不被 403（mock DB连接避免挂起）"""
         group, instance = group_with_permissions
         await db.execute(
             user_groups.insert().values(
@@ -254,12 +257,38 @@ class TestPermissionEndpointIntegration:
         token = create_access_token(
             data={"sub": str(developer_user.id), "role": developer_user.role}
         )
-        resp = await client.post(
-            "/api/v1/query",
-            json={"instance_id": instance.id, "database": "test", "sql": "SELECT 1"},
-            headers={"Authorization": f"Bearer {token}"},
-        )
-        # 不应是 403（可能 400/500 因为连不上真DB，但权限通过）
+
+        # Mock aiomysql 防止真实连接挂起（见 skill #20, #37）
+        mock_cursor = AsyncMock()
+        mock_cursor.description = [("1",)]
+        mock_cursor.fetchall.return_value = [{"1": 1}]
+        mock_cursor.close = AsyncMock()
+
+        @asynccontextmanager
+        async def mock_cursor_ctx(*a, **kw):
+            yield mock_cursor
+
+        mock_conn = AsyncMock()
+        mock_conn.cursor = mock_cursor_ctx
+        mock_conn.commit = AsyncMock()
+        mock_conn.rollback = AsyncMock()
+        mock_conn.close = AsyncMock()
+
+        mock_aiomysql = MagicMock()
+        mock_aiomysql.connect = AsyncMock(return_value=mock_conn)
+        mock_aiomysql.DictCursor = MagicMock()
+
+        with patch.dict(sys.modules, {"aiomysql": mock_aiomysql}):
+            resp = await client.post(
+                "/api/v1/query",
+                json={
+                    "instance_id": instance.id,
+                    "database": "test",
+                    "sql": "SELECT 1",
+                },
+                headers={"Authorization": f"Bearer {token}"},
+            )
+        # 不应是 403（权限通过，mock 返回成功）
         assert resp.status_code != 403
 
     @pytest.mark.asyncio