pytest中monkey-patch外部API函数报错AttributeError的问题排查

我正在使用pytest为以下函数编写测试用例：

def function_to_testcase(conn, event, customer):
   if customer["userStatus"] is None:
       raise IncompleteSignup("Customer marked as Incomplete Signup")
   logger.info("Forgot password flow started")
   send_update_customer_details_message(
       db_id=customer["cid"],
       zu_id=customer["AccountId"],
       email=customer["UserName"],
       encrypted_password=customer["Password"],
       skip_targets=True,
   )

需要对外部API调用函数send_update_customer_details_message进行monkey-patch，编写的测试用例如下：

import pytest
import unittest
from customers_migration.flows.legacy import (
    run_legacy_forgot_password_flow,
)
class TestLegacy(unittest.TestCase):
    monkeypatch = pytest.MonkeyPatch()
    MSG = "Forgot password flow for Legacy started"
    event_trigger_other = {
        "request": {"password": "test_pwd"},
        "triggerSource": "Other",
    }
    customer_status = {
        "userStatus": 2,
        "Password": "Test1ngpa$",
        "cid": 1,
        "AccountId": "12312",
        "UserName": "test@test.com",
    }

    def test_run_forgot_password_flow_logger(self):
        with self.assertLogs() as captured:
            self.monkeypatch.setattr(
                run_legacy_forgot_password_flow,
                "send_update_customer_details_message",
                None,
            )
            run_ipv_legacy_forgot_password_flow(
                "", self.event_trigger_other, self.customer_status
            )
        self.assertEqual(len(captured.records), 1)
        self.assertEqual(
            self.MSG,
            captured.records[0].getMessage(),
        )

运行时报错：

AttributeError: <function run_legacy_forgot_password_flow at 0x7fc75f780280> has no attribute 'send_update_customer_details_message'

核心错误原因 #

你错误地尝试给函数对象run_legacy_forgot_password_flow添加属性send_update_customer_details_message，但该函数本身并不具备这个属性。Monkey-patch的正确目标应该是send_update_customer_details_message被导入的模块，而非调用它的函数。

具体修正步骤 #

1. 修正Monkey-patch的目标
   找到send_update_customer_details_message所在的模块（假设它在customers_migration.flows.legacy中，或被导入到该模块），将setattr的第一个参数改为对应模块：

   # 先导入目标模块
   from customers_migration.flows import legacy
   
   # 测试中修改patch目标
   self.monkeypatch.setattr(
       legacy,  # 目标模块，而非函数
       "send_update_customer_details_message",
       lambda *args, **kwargs: None  # 用空lambda替代原函数，避免执行实际API调用
   )
   

   注意：如果send_update_customer_details_message是从其他模块导入到legacy的，仍然需要patchlegacy模块中的这个引用，而非原模块。

2. 修正函数调用笔误
   测试中调用的run_ipv_legacy_forgot_password_flow与导入的run_legacy_forgot_password_flow名称不符，需改为正确的函数名：

   run_legacy_forgot_password_flow(
       "", self.event_trigger_other, self.customer_status
   )
   

3. 统一日志断言内容
   被测试函数输出的日志是"Forgot password flow started"，但测试中定义的MSG是"Forgot password flow for Legacy started"，两者不匹配会导致断言失败，需统一日志字符串。

4. 优化Monkey-patch使用方式
   直接在类中定义monkeypatch = pytest.MonkeyPatch()不是最佳实践，建议在测试方法内创建实例并手动撤销，或使用pytest的monkeypatch fixture：

   def test_run_forgot_password_flow_logger(self):
       monkeypatch = pytest.MonkeyPatch()
       try:
           monkeypatch.setattr(legacy, "send_update_customer_details_message", lambda *args, **kwargs: None)
           with self.assertLogs() as captured:
               run_legacy_forgot_password_flow("", self.event_trigger_other, self.customer_status)
           # 执行断言逻辑
       finally:
           monkeypatch.undo()  # 确保patch被撤销，不影响其他测试
   

内容的提问来源于stack exchange，提问作者Prinz Piuz