Python-模拟操作系统错误异常

尝试使用副作用模拟Python 3.6中的PermissionError异常。看起来调用了我的函数并引发了EPERM异常，但随后它无法运行我的except语句。对于“真实”OS错误异常，运行的代码与预期的相同。我的代码：

#my_module.py
import os
import errno  
import sys
import inspect

def open_file(fname):
    try:
        with open('./' + fname, 'w') as f:
            print('never get here')
        return(0)

    except PermissionError as e:
        print('ERROR: \nIn function: ' + inspect.stack()[0][3])
        print('On line: {}'.format(sys.exc_info()[-1].tb_lineno), type(e).__name__, e)
        sys.exit(1)

我的测试：

#OpenFileMockTestCase.py
from unittest import TestCase
from unittest import mock
import errno
import my_module

class OpenFileMockTestCase(TestCase):

    @mock.patch('my_module.os.open')
    def test_2_open_file_mock_oserror(self, mock_oserror):
        with self.assertRaises(SystemExit):
            mock_oserror.my_module.open_file.side_effect = (OSError((errno.EPERM), 'Not Allowed'))
            print('starting open_file with testfile2.txt...')
            mock_oserror.my_module.open_file('testfile2.txt')

当我跑步时：

C:\Users\mylib>coverage3 run -m unittest OpenFileMockTestCase.py -v
test_2_open_file_mock_oserror (OpenFileMockTestCase.OpenFileMockTestCase) ... starting open_file with testfile2.txt...

ERROR

======================================================================
ERROR: test_2_open_file_mock_oserror (OpenFileMockTestCase.OpenFileMockTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "c:\users\xti027\appdata\local\programs\python\python36\lib\unittest\mock.py", line 1179, in patched
    return func(*args, **keywargs)
  File "C:\Users\xti027\Documents\DataTool-Git\DataTool\DataLoaderConfig\OpenFileMockTestCase.py", line 14, in test_2_open_file_mock_oserror
    mock_oserror.my_module.open_file('testfile2.txt')
  File "c:\users\xti027\appdata\local\programs\python\python36\lib\unittest\mock.py", line 939, in __call__
    return _mock_self._mock_call(*args, **kwargs)
  File "c:\users\xti027\appdata\local\programs\python\python36\lib\unittest\mock.py", line 995, in _mock_call
    raise effect
PermissionError: [Errno 1] Not Allowed

----------------------------------------------------------------------
Ran 1 test in 0.031s

FAILED (errors=1)

我已经阅读了一些关于异常和模仿的问题和回答，并查看了Python文档：

---

我在正确的地方模仿正确的东西吗

您只需提出

PermissionError

异常：

mock_oserror.side_effect = PermissionError

请注意，我们直接在模拟的

open（）

调用上设置了副作用！我还将模拟测试模块中的全局

open（）

名称，而不是

os.open

您还应该直接调用被测函数，而不是作为

mock\u oserror

对象的属性：

import my_module

# ....

@mock.patch('my_module.open')
def test_2_open_file_mock_oserror(self, mock_open):
    mock_open.side_effect = PermissionError
    print('starting open_file with testfile2.txt...')
    with self.assertRaises(SystemExit):
        my_module.open_file('testfile2.txt')

我在这里使用了名称

mock\u open

，因为这更好地反映了被嘲笑的内容

演示：

---

对我来说是完美的结果。感谢您对代码的清理和清晰的解释。

>>> import os
>>> import errno
>>> import sys
>>> import inspect
>>> from unittest import mock
>>> def open_file(fname):
...     try:
...         with open('./' + fname, 'w') as f:
...             print('never get here')
...         return(0)
...     except PermissionError as e:
...         print('ERROR: \nIn function: ' + inspect.stack()[0][3])
...         print('On line: {}'.format(sys.exc_info()[-1].tb_lineno), type(e).__name__, e)
...         sys.exit(1)
...
>>> with mock.patch('__main__.open') as mock_oserror:
...     mock_oserror.side_effect = PermissionError
...     try:
...         open_file('testfile2.txt')
...     except SystemExit:
...         print('test passed, sys.exit() called')
...
ERROR:
In function: open_file
On line: 3 PermissionError
test passed, sys.exit() called