关于单元测试：Python – 模拟操作系统错误异常

Python - Mocking OS Error Exception

尝试使用side_effect在Python 3.6中模拟PermissionError异常。看起来我的函数被调用并且引发了EPERM异常，但是它无法运行我的except语句。对于"真正的"OSError异常，相同的代码按预期运行。我的代码：

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#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:
In 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：

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#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：

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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)

我已经阅读了几个关于异常和模拟的SO问题和回答，比如我如何为OSError编写单元测试？并查看了Python文档：https：//docs.python.org/3.6/library/unittest.mock.html#module-unittest.mock
我在正确的地方嘲笑合适的物品吗？

你可以提出PermissionError异常：

1	mock_oserror.side_effect = PermissionError

请注意，我们直接在模拟open()调用上设置副作用！我还会在被测模块中模拟全局open()名称，而不是os.open。

您还应该直接调用函数测试，而不是作为mock_oserror对象的属性：

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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_open，因为它更好地反映了被嘲笑的内容。

演示：

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>>> 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:
In 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