python - 如何模拟你的功能？

Question

我不知道如何在 python 中模拟我的函数，我尝试寻找一些代码，但似乎都不起作用，请考虑以下布局:

| project.py
| tests.py

project.py:

def foobar():
    return

tests.py:

import unittest
from unittest.mock import patch
import os

from project import foobar

def os_urandom_mock():
    return 'mocked'

def foobar_mock():
    return 'mocked'


class TestProject(unittest.TestCase):

    # mocked os.urandom worked well
    @patch('os.urandom', side_effect=os_urandom_mock)
    def test_os_urandom_mocked(self, os_urandom_mocked):
        self.assertEqual(os.urandom(), 'mocked')

    # but this doesn't
    @patch('project.foobar', side_effect=foobar_mock)
    def test_foobar_mocked(self, foobar_mocked):
        self.assertEqual(foobar(), 'mocked')

    # and this also doesn't work
    @patch('project.foobar')
    def test_foobar_mocked_another(self, foobar_mocked):
        foobar_mocked.return_value = 'mocked'
        self.assertEqual(foobar(), 'mocked')

    # and this also doesn't work
    def test_foobar_mocked_last_try(self):
        with patch('project.foobar') as foobar_mocked:
            foobar_mocked.return_value = 'mocked'
            self.assertEqual(foobar(), 'mocked')

unittest.main()

所以，python3测试.py:

======================================================================
FAIL: test_foobar_mocked (__main__.TestProject)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Python36\lib\unittest\mock.py", line 1179, in patched
    return func(*args, **keywargs)
  File "tests.py", line 24, in test_foobar_mocked
    self.assertEqual(foobar(), 'mocked')
AssertionError: None != 'mocked'

======================================================================
FAIL: test_foobar_mocked_another (__main__.TestProject)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "C:\Python36\lib\unittest\mock.py", line 1179, in patched
    return func(*args, **keywargs)
  File "tests.py", line 30, in test_foobar_mocked_another
    self.assertEqual(foobar(), 'mocked')
AssertionError: None != 'mocked'

======================================================================
FAIL: test_foobar_mocked_last_try (__main__.TestProject)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests.py", line 35, in test_foobar_mocked_last_try
    self.assertEqual(foobar(), 'mocked')
AssertionError: None != 'mocked'

----------------------------------------------------------------------
Ran 4 tests in 0.002s

FAILED (failures=3)

如您所见，test_os_urandom_mocked 没问题，但是我尝试模拟我的 foobar 函数的所有其他测试都失败了，不知道为什么，任何人都可以吗？请解释一下是否可以这样做？

Answer 1

您可以通过模块引用修补后的函数来完成此工作:

import unittest
from unittest.mock import patch
import os
import project

def os_urandom_mock():
    return 'mocked'

def foobar_mock():
    return 'mocked'


class TestProject(unittest.TestCase):

    @patch('os.urandom', side_effect=os_urandom_mock)
    def test_os_urandom_mocked(self, os_urandom_mocked):
        self.assertEqual(os.urandom(), 'mocked')

    @patch('project.foobar', side_effect=foobar_mock)
    def test_foobar_mocked(self, foobar_mocked):
        self.assertEqual(project.foobar(), 'mocked')

    @patch('project.foobar')
    def test_foobar_mocked_another(self, foobar_mocked):
        foobar_mocked.return_value = 'mocked'
        self.assertEqual(project.foobar(), 'mocked')

    def test_foobar_mocked_last_try(self):
        with patch('project.foobar') as foobar_mocked:
            foobar_mocked.return_value = 'mocked'
            self.assertEqual(project.foobar(), 'mocked')

unittest.main()

这里要注意的关键是，当您给 patch 一个字符串时，它会替换该路径上的引用。这种行为得到了很好的证明 here 。 (感谢 wholevinski 提供链接。)

根据您现在的代码，测试文件中的 foobar 引用原始函数，因为您在补丁到位之前导入了它。相比之下，如果您通过模块引用它，则将始终使用模块的引用。

或者，您可以执行 wholevinski 操作在评论中建议，并让您的补丁替换当前范围内的引用，而不是其原始模块中的引用:

import unittest
from unittest.mock import patch
import os
from project import foobar

def os_urandom_mock():
    return 'mocked'

def foobar_mock():
    return 'mocked'


class TestProject(unittest.TestCase):
    @patch(__name__ + '.foobar', side_effect=foobar_mock)
    def test_foobar_mocked(self, foobar_mocked):
        self.assertEqual(foobar(), 'mocked')

    @patch(__name__ + '.foobar')
    def test_foobar_mocked_another(self, foobar_mocked):
        foobar_mocked.return_value = 'mocked'
        self.assertEqual(foobar(), 'mocked')

    def test_foobar_mocked_last_try(self):
        with patch(__name__ + '.foobar') as foobar_mocked:
            foobar_mocked.return_value = 'mocked'
            self.assertEqual(foobar(), 'mocked')

unittest.main()

请注意，在大多数情况下，您将修补被测试模块导入的某些内容，而不是直接在测试中调用修补的函数。在这种情况中，事情往往会变得更加清晰:

asdf.py:

def baz():
    return 'baz'

project.py:

from asdf import baz

def foobar():
    return baz()

测试.py:

import unittest
from unittest.mock import patch
import os
from project import foobar

def baz_mock():
    return 'mocked'

class TestProject(unittest.TestCase):
    @patch('project.baz', side_effect=baz_mock)
    def test_foobar_mocked(self, foobar_mocked):
        self.assertEqual(foobar(), 'mocked')

    @patch('project.baz')
    def test_foobar_mocked_another(self, baz_mocked):
        foobar_mocked.return_value = 'mocked'
        self.assertEqual(foobar(), 'mocked')

    def test_foobar_mocked_last_try(self):
        with patch('project.baz') as baz_mocked:
            foobar_mocked.return_value = 'mocked'
            self.assertEqual(foobar(), 'mocked')

unittest.main()