模拟 subprocess.Popen 依赖于导入样式

2022-01-18 00:00:00 python subprocess popen mocking unit-testing

问题描述

在尝试模拟 Popen 时，只有在单元测试代码和主模块代码中子流程的导入匹配时，我才能使其成功.

When attempting to mock Popen I can only get it to succeed if the importing of subprocess matches in both unit test code and main module code.

给定以下模块 listdir.py:

Given following module listdir.py:

from subprocess import Popen, PIPE

def listdir(dir):
    cmd = ['ls', dir]
    pc = Popen(cmd, stdout=PIPE, stderr=PIPE)
    out, err = pc.communicate()
    if pc.returncode != 0:
        raise Exception
    return out

以及下面的单元测试代码test_listdir.py

and following unit test code test_listdir.py

import subprocess
import listdir
import mock

@mock.patch.object(subprocess, 'Popen', autospec=True)
def test_listdir(mock_popen):
    mock_popen.return_value.returncode = 0
    mock_popen.return_value.communicate.return_value = ("output", "Error")
    listdir.listdir("/fake_dir")

由于某些原因，Popen 没有被模拟，因为两个 python 模块之间的导入样式不同，并且运行测试总是引发异常.

For some reason Popen is not being mocked, due to the import style being different between the two python modules, and running the test always raises an exception.

如果我更改 listdir.py 以导入所有子进程，例如

If I change listdir.py to import all of subproces e.g.

import subprocess

def listdir(dir):
    cmd = ['ls', dir]
    pc = subprocess.Popen(cmd, stdout=subprocess.PIPE, 
                          stderr=subprocess.PIPE)
    out, err = pc.communicate()
    if pc.returncode != 0:
        raise ListingErrorException
    return out

然后在测试中返回输出".

Then "output" is returned in the test.

任何人都想解释一下为什么，我的偏好是from subprocess import Popen, Pipe in 这两个模块，但我就是无法模拟.

Anyone care to shed some light on why, my preference would be to have from subprocess import Popen, Pipe in both modules, but I just can't get that to mock.

解决方案

你需要在 listdir 中修补 Popen 的副本，而不是你刚刚导入的那个.所以，不要使用 @mock.patch.object(subprocess, 'Popen', autospec=True)，试试 @mock.patch.object(listdir, 'Popen', autospec=True)

You need to patch the copy of Popen in listdir, not the one you just imported. So, instead of @mock.patch.object(subprocess, 'Popen', autospec=True), try @mock.patch.object(listdir, 'Popen', autospec=True)

有关详细信息，请参阅此文档:http://www.voidspace.org.uk/python/mock/patch.html#where-to-patch

See this doc for more info: http://www.voidspace.org.uk/python/mock/patch.html#where-to-patch

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