为什么我的班级在我的单元测试中没有被嘲笑？

Question

我正在尝试模拟 GetDatabaseConnection，但它仍在其中运行代码。

class GetDatabaseConnection:
    resp_dict = json.loads(get_secret())
    endpoint = resp_dict.get('host')
    username = resp_dict.get('username')
    password = resp_dict.get('password')
    database_name = resp_dict.get('dbname')
    port = resp_dict.get('port')
    connection = pymysql.connect(host=endpoint, user=username, passwd=password, db=database_name, port=port)
    cursor = connection.cursor()

这是我编写的用来模拟类的测试。

    @mock.patch("lambda_function.GetDatabaseConnection")
    def test_mock_simple_class(mock_class):
        mock_class.return_value = "test"

但我收到以下错误

test_lambda_function.py::TestPreSignUp::test_mock_simple_class FAILED    [100%]
test_lambda_function.py:151 (TestPreSignUp.test_mock_simple_class)
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/unittest/mock.py:1334: in patched
    with self.decoration_helper(patched,
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/contextlib.py:117: in __enter__
    return next(self.gen)
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/unittest/mock.py:1316: in decoration_helper
    arg = exit_stack.enter_context(patching)
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/contextlib.py:429: in enter_context
    result = _cm_type.__enter__(cm)
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/unittest/mock.py:1389: in __enter__
    self.target = self.getter()
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/unittest/mock.py:1564: in <lambda>
    getter = lambda: _importer(target)
/Library/Frameworks/Python.framework/Versions/3.9/lib/python3.9/unittest/mock.py:1236: in _importer
    thing = __import__(import_path)
../lambda_function.py:42: in <module>
    class GetDatabaseConnection():
../lambda_function.py:43: in GetDatabaseConnection
    resp_dict = json.loads(get_secret())

Answer 1

您遇到的问题与关于importing without executing the class - python 的其他问题相同。由于您将类设计为具有可以执行对pymysql 的调用的属性，因此即使刚刚导入文件（例如在模拟修补期间），它们也会立即执行，甚至无需创建GetDatabaseConnection 的实例。

src.py

import pymysql


class GetDatabaseConnection:
    connection = pymysql.connect(host="127.0.0.1", user='username', passwd="password", db='database_name', port=80)

test_src.py

from unittest import mock

# This will read your class. And this will run your <pymsql> commands even without a running patch yet.
import src  # or <from src import GetDatabaseConnection>


# This will also read your class with or without the import above. And this will run your <pymsql> commands even without the patch yet.
@mock.patch('src.GetDatabaseConnection')
def test_try1():
    assert True

输出

$ pytest -q -rP

================================================================================================= ERRORS ==================================================================================================
______________________________________________________________________________________ ERROR collecting test_samp.py
E   pymysql.err.OperationalError: (2003, "Can't connect to MySQL server on '127.0.0.1' ([Errno 111] Connection refused)")
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
1 error in 0.22s

解决方案 1：

通过将类放在类方法中，重新设计类以不执行类级逻辑。

class GetDatabaseConnection:
    def __init__(self):
        self.connection = pymysql.connect(host="127.0.0.1", user='username', passwd="password", db='database_name', port=80)

from unittest import mock


@mock.patch('src.GetDatabaseConnection')
def test_try(mock_class):
    assert True

$ pytest -q -rP
================================================================================================= PASSES ==================================================================================================
1 passed in 0.03s

解决方案 2：

将您的GetDatabaseConnection 转换为普通函数：

def getDatabaseConnection():
    return {
        "connection": pymysql.connect(host="127.0.0.1", user='username', passwd="password", db='database_name', port=80),
    }

from unittest import mock


@mock.patch('src.getDatabaseConnection')
def test_try(mock_func):
    assert True

• 输出与解决方案 1 相同

解决方案 3：

不推荐。不要在没有运行补丁的情况下直接导入文件。因此，也不要修补类GetDatabaseConnection 以避免从文件中读取并执行pymysql。首先，您需要在导入文件之前修补pymysql。这很难维护，如果您的源代码文件之一导入包含GetDatabaseConnection 类的文件，则会中断。

from unittest import mock


@mock.patch('pymysql.connect')
def test_try(mock_pymsql):
    import src  # Or <from src import GetDatabaseConnection>
    print(f"{src.GetDatabaseConnection.connection=}")  # This will be the patched version
    assert True

输出：

$ pytest -q -rP
================================================================================================= PASSES ==================================================================================================
________________________________________________________________________________________________ test_try _________________________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
src.GetDatabaseConnection.connection=<MagicMock name='connect()' id='139647536711760'>
1 passed in 0.03s