feat: change segment_size to decimal in Product model

business/tests.py

@@ -4,7 +4,7 @@ from concurrent.futures import ThreadPoolExecutor
 
 from django.contrib.auth import get_user_model
 from django.test import TestCase, TransactionTestCase, override_settings
-from django.db import connections
+from django.db import connections, close_old_connections
 from django.utils import timezone
 from unittest.mock import patch, MagicMock
 
@@ -1240,11 +1240,17 @@ class SalesOrderConcurrencyTestCase(TransactionTestCase):
 
     def test_concurrent_sales_order_approval_updates_balance_once(self):
         def approve():
-            services.review_sales_order(
-                sales_order_id=self.sales_order.id,
-                target_status=business_models.SalesOrderStatusEnum.APPROVED,
-                reviewed_by=self.user,
-            )
+            # ThreadPoolExecutor 会复用线程；Django 的 DB connection 是线程局部的，
+            # 若不显式关闭，可能导致测试 DB 在 teardown 时仍被占用，无法 DROP。
+            close_old_connections()
+            try:
+                services.review_sales_order(
+                    sales_order_id=self.sales_order.id,
+                    target_status=business_models.SalesOrderStatusEnum.APPROVED,
+                    reviewed_by=self.user,
+                )
+            finally:
+                connections.close_all()
 
         with ThreadPoolExecutor(max_workers=2) as executor:
             futures = [executor.submit(approve) for _ in range(2)]