如何使用 Mock 修补 OS.mkdir？答案

【问题标题】：How to patch OS.mkdir with Mock?如何使用 Mock 修补 OS.mkdir？
【发布时间】：2014-09-02 12:31:51
【问题描述】：

我正在尝试使用带有 pytest 的 Mock 模块进行单元测试。

我希望 os.path.isdir() 返回 False，并且 os.mkdir() 不运行；我只是想验证传递给它的参数是否正确。

我想你只需要看set_path方法

我的应用：

import pytumblr, os, sys, prowlpy, json, collections
from urllib2 import urlopen
from time import sleep
from apiclient.discovery import build

class Site(object):
    """A generic site."""
    def __init__(self, user):
        self.user = user

    def set_path(self):
        if os.path.isdir(self.user_dir):            # if user dir already exists
            print "**Directory already exists: ", self.user_dir
        else:
            os.mkdir(self.user_dir)                 # else create user dir
            print "Created Directory: ", self.user_dir

class Tumblr(Site):
    """A tumblr blog."""
    type = "tumblr"
    type_dir = os.path.join(os.getcwd(), type)
    def __init__(self, user):
        super(Tumblr, self).__init__(user)
        self.user_dir = os.path.join(Tumblr.type_dir, self.user)

我的测试总是失败，如下所示：

import tumblrip_new as tum
import mock

    @mock.patch('tumblrip_new.os')
    @mock.patch('tumblrip_new.os.path')
    def test_create_new_user_dir(self, mock_path, mock_os):
        """Creates a directory if one does not exist."""
        t = tum.Tumblr("username")
        # directory does not exist:
        mock_path.isdir.return_value = False
        t.set_path()
        mock_os.mkdir.assert_called_with(t.user_dir)

输出显示失败的原因：

_mock_self = <MagicMock name='os.mkdir' id='33647664'>
args = (<MagicMock name='os.path.join()' id='33568048'>,), kwargs = {}
self = <MagicMock name='os.mkdir' id='33647664'>
expected = "mkdir(<MagicMock name='os.path.join()' id='33568048'>)"

>   ???
E   AssertionError: Expected call: mkdir(<MagicMock name='os.path.join()' id='3
568048'>)
E   Not called

build\bdist.win32\egg\mock.py:831: AssertionError
===================== 1 failed, 3 passed in 0.22 seconds ======================

【问题讨论】：

标签： python unit-testing python-2.7 mocking

【解决方案1】：

我通过以下方式修复它：

@mock.patch('tumblrip_new.os.path')
@mock.patch('tumblrip_new.os')
def test_create_new_user_dir(self, mock_os, mock_path):
    """Creates a directory if one does not exist."""
    t = tum.Tumblr("username")
    # directory does not exist:
    mock_path.isdir.return_value=False
    t.set_path()
    mock_os.mkdir.assert_called_with(t.user_dir)

【讨论】：

【解决方案2】：

使用副作用更新模拟行为（os.path.isdir）：

import os
import unittest
from mock import Mock, MagicMock, patch
from contextlib import nested

"""Creates a directory if one does not exist."""


class Site(object):
    """A generic site."""
    def __init__(self, user):
        self.user = user

    def set_path(self):
        if os.path.isdir(self.user_dir):            # if user dir already exists
            print "**Directory already exists: ", self.user_dir
        else:
            os.mkdir(self.user_dir)                 # else create user dir
            print "Created Directory: ", self.user_dir


class Tumblr(Site):
    """A tumblr blog."""
    type = "tumblr"
    type_dir = os.path.join(os.getcwd(), type)

    def __init__(self, user):
        super(Tumblr, self).__init__(user)
        self.user_dir = os.path.join(Tumblr.type_dir, self.user)


class testCreateDir(unittest.TestCase):

    def test_create_new_user_dir(self):

        os = MagicMock()
        os.path = MagicMock()

        os.path.isdir = Mock(return_value=False)
        os.path.join = Mock(return_value="user_dir")

        mkdir = Mock()

        def update_status(*args):
            mkdir(args[0])
            os.path.isdir.return_value = True

        os.mkdir = Mock(side_effect=update_status)

        with nested(patch('os.path', os.path), patch('os.mkdir', os.mkdir)):
            t = Tumblr("username")
            t.set_path()
            mkdir.assert_called_with(t.user_dir)
            t.set_path()
            t.set_path()
            t.set_path()
            mkdir.assert_called_once_with(t.user_dir)

【讨论】：