如何模拟 multiprocessing.Event.is_set() - AttributeError

Question

我正在尝试模拟一个 multiprocessing.Event 对象，以便对 event.is_set() returns 的调用在第一次迭代时为 False，在第二次迭代时为 true。我在以下尝试中失败了：

import unittest
import unittest.mock as mock
import multiprocessing


class MyClassUnderTest:
    def __init__(self):
        self.event = multiprocessing.Event()
        # start a Process which immediately uses self.event

    def my_method_under_test(self):
        while not self.event.is_set():
            pass  # do something
        return True


class TestMyClassUnderTest(unittest.TestCase):
    @mock.patch.object(multiprocessing.Event, 'is_set', return_value=False)
    def test_my_method(self, mock_event):
        mock_event.side_effect = [False, True]

        myobj = MyClassUnderTest()
        self.assertTrue(myobj.my_method_under_test())

我遇到了错误：

AttributeError: <bound method BaseContext.Event of <multiprocessing.context.DefaultContext object at 0x7f1068a50e48>> does not have the attribute 'is_set'

我无法覆盖 MyClassUnderTest.event 因为事件对象会立即使用，所以我试图覆盖整个 multiprocessing.Event class.

Answer 1

这是一种使用 configure_mock 的方法：

import unittest
import unittest.mock as mock
import multiprocessing


class MyClassUnderTest:
    def __init__(self):
        self.event = multiprocessing.Event()
        # start a Process which immediately uses self.event

    def my_method_under_test(self):
        while not self.event.is_set():
            pass  # do something
        return True


class TestMyClassUnderTest(unittest.TestCase):
    @mock.patch('multiprocessing.Event')
    def test_my_method(self, mock_event):
        mock_event.configure_mock(**{'is_set.side_effect': [False, True]})

        myobj = MyClassUnderTest()
        self.assertTrue(myobj.my_method_under_test())

如果有人知道如何将其完全压缩成 @mock.patch(...)，那仍然有用。

Answer 2

为了响应@David Parks 的号召，这里有一个简化的工作示例。

import unittest
import unittest.mock as mock
import multiprocessing


class MyClassUnderTest:
    def __init__(self):
        self.event = multiprocessing.Event()
        # start a Process which immediately uses self.event

    def my_method_under_test(self):
        while not self.event.is_set():
            pass  # do something
        return True


class TestMyClassUnderTest(unittest.TestCase):
    @mock.patch('multiprocessing.Event')
    def test_my_method(self, mock_event):
        mock_event.is_set.side_effect = [False, True]

        myobj = MyClassUnderTest()
        self.assertTrue(myobj.my_method_under_test())

诀窍是仅在装饰器中修补 Event class，并在测试主体中模拟 is_set() 的响应。老实说，我不知道为什么我们不能直接修补 multiprocessing.Event.is_set，因为 multiprocessing.Event 是 threading.Event 的克隆。

如何模拟 multiprocessing.Event.is_set() - AttributeError

How to mock multiprocessing.Event.is_set() - AttributeError

python

python-unittest

magicmock