magic_mock_db.connect.assert_called() 失败，即使它被调用

Question

我正在使用vscode-python的扩展和python的unittest来测试peewee是否成功连接到数据库。 这是正在测试的类：

import logging
from datetime import (datetime, timezone)
# 3rd party libraries
import peewee

log_fmt = "%(asctime)s - %(funcName)s - %(name)s - %(levelname)s - %(message)s"
# enable logging
logging.basicConfig(
format=log_fmt,
level=logging.INFO
)
logger = logging.getLogger(__name__)

class Freezer():
db_name = "db"
db_username = "db_user"
db_pswd = "db_pswd"
def __init__(self):
self.freezer = peewee.MySQLDatabase(
database=Freezer.db_name,
user=Freezer.db_username,
password=Freezer.db_pswd,
host="localhost",
port=3306
)
def open_freezer(self):
if self.freezer.connect():
print('CONNECTED')

调用时open_freezer()将连接到数据库并打印出CONNECTED。 这是测试套件：

import unittest
from unittest.mock import (MagicMock, patch)
from src.freezer import (Freezer, BaseModel, PlatiniumBotUser, peewee)

class FreezerTestSuites(unittest.TestCase):
def test_open_freezer(self):
with patch("src.freezer.peewee.MySQLDatabase", autospec=True) as mock_db:
self.freezer = Freezer()
mock_db.assert_called_once()
self.freezer.open_freezer()
mock_db.connect.assert_called()

在最后一行中，akamock_db.connect.assert_called()失败，并显示以下AssertionError：

test_open_freezer (test_freezer.FreezerTestSuites) ... 
CONNECTED
FAIL
NoneType: None
======================================================================
FAIL: test_open_freezer (test_freezer.FreezerTestSuites)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/gadd/vscodeworkspace/db_testing/tests/test_freezer.py", line 23, in test_open_freezer
mock_db.connect.assert_called()
File "/usr/lib/python3.8/unittest/mock.py", line 882, in assert_called
raise AssertionError(msg)
AssertionError: Expected 'connect' to have been called.
----------------------------------------------------------------------
Ran 1 test in 0.117s
FAILED (failures=1)

正如您可以清楚地看到的那样，它打印出CONNECTED从而指示它已调用connect()方法并成功连接，但断言失败。

我做错了什么？

提前谢谢。

Answer 1

根据 jonrsharpe，我在模拟类mock_db上调用connect，而不是它应该返回self.freezer。正确的方法是：

def test_open_freezer(self):
with patch("peewee.MySQLDatabase", autospec=True) as mock_db:
self.freezer = Freezer()
mock_db.assert_called()
self.freezer.open_freezer()
mock_db.return_value.connect.assert_called()