mock.patch与多处理

Question

我很难在多处理环境中使用mock.patch，而没有多处理的mock.patch工作得很好。文件名：test_mp.py

import multiprocessing
import mock

def inner():
    return sub()

def sub():
    return "abc"

def test_local():
    assert inner()=="abc"

def test_mp():    
    with multiprocessing.Pool() as pool:
        assert pool.apply(inner,args=[])=='abc'

def test_mock():    
    with mock.patch('test_mp.sub', return_value='xxx') as xx:
        assert inner()=="xxx"
        xx.assert_called_once()

def test_mp_mock():    
    with multiprocessing.Pool() as pool:
        with mock.patch('test_mp.sub', return_value='xyz') as xx:
            assert pool.apply(inner,args=[])=='xyz'
            xx.assert_called_once()

• Test test_local，test_mock和test_mock完成了

的test_mp_mock测试失败

=================================== FAILURES ===================================
_________________________________ test_mp_mock _________________________________

    def test_mp_mock():
        with multiprocessing.Pool() as pool:
            with mock.patch('test_mp.sub', return_value='xyz') as xx:
>               assert pool.apply(inner,args=[])=='xyz'
E               AssertionError: assert 'abc' == 'xyz'
E                 - abc
E                 + xyz

projects/mfhealth/test_mp.py:25: AssertionError

更新：

在https://medium.com/uckey/how-mock-patch-decorator-works-in-python-37acd8b78ae的基础上，在sharedmock https://github.com/elritsch/python-sharedmock的帮助下，我能够更进一步，但仍未完成。

我将test_mp.py扩展为

from sharedmock.mock import SharedMock

def inner2(sm):
    with mock.patch('test_mp.sub', sm) as xx:
        return inner()


def test_mp_smock():
    with multiprocessing.Pool() as pool:
        sm=SharedMock()
        sm.return_value="xyz"
        with mock.patch('test_mp.sub', sm) as xx:
            assert pool.apply(inner2,args=[sm])=='xyz'
            assert xx.call_count == 1

def test_mp_mock2():
    with multiprocessing.Pool() as pool:
        sm=mock.Mock()
        sm.return_value="xyz"
        print(f"before patch {sub}, {locals()}")
        with mock.patch('test_mp.sub', sm) as xx:
            print(f"after patch {sub}")
            assert pool.apply(inner2,args=[sm])=='xyz'
            assert xx.call_count == 1

取得了以下结果：

• test_mp_smock用_pickle.PicklingError: Can't pickle <class 'mock.mock.Mock'>: it's not the same object as mock.mock.Mock

完成successfully.

• test_mp_mock2失败

test_mp_smock的主要缺点是必须引入一种新的方法inner2来通过mock.patch激活补丁。任何关于如何将补丁从test_mp_smock传播到正在测试的代码而不引入包装器方法inner2的想法，因为我不能覆盖。

pool.apply(inner,args=[])

Answer 1

终于，我让它起作用了。

SharedMock并不像Mock那样灵活。缺少assert_called_once_with，.，但是可以设置返回的值或检查调用的次数或其参数。

import multiprocessing
import mock
from sharedmock.mock import SharedMock


def inner():
    return sub(x="xxx")

def sub(x=""):
    return f"abc"

def fun_under_test():
    with multiprocessing.Pool() as pool:
        assert pool.apply(inner,args=[])=='xyz'

def test_final():
    sm=SharedMock()
    sm.return_value="xyz"
    with mock.patch('test_mp.sub', sm) as xx:
        fun_under_test()
        assert xx.call_count == 1 #number of calls of sub function
        assert xx.mock_calls[0][2]['x']=="xxx" # value of parameters ie sub(x="xxx")