Python-嘲笑OS错误异常

Question

尝试使用side_effect模拟python 3.6中的常规异常。看来我的功能被调用，并且提高了eperm异常，但后来无法运行我的语句。对于"真实" Oserror异常的预期，相同的代码运行。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')

我运行时：

C:Usersmylib>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:usersxti027appdatalocalprogramspythonpython36libunittestmock.py", line 1179, in patched
    return func(*args, **keywargs)
  File "C:Usersxti027DocumentsDataTool-GitDataToolDataLoaderConfigOpenFileMockTestCase.py", line 14, in test_2_open_file_mock_oserror
    mock_oserror.my_module.open_file('testfile2.txt')
  File "c:usersxti027appdatalocalprogramspythonpython36libunittestmock.py", line 939, in __call__
    return _mock_self._mock_call(*args, **kwargs)
  File "c:usersxti027appdatalocalprogramspythonpython36libunittestmock.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例外的问题和回答，并嘲笑我该如何为Oserror编写单位测试？并查看Python Doc：https：//docs.python.org/3.6/library/unittest.mock.html#module-unittest.mock我在正确的位置嘲笑正确的物品吗？

Answer 1

您可以提高PermissionError例外：

mock_oserror.side_effect = PermissionError

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

您还应该直接调用函数，而不是作为mock_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_open，因为这样可以更好地反映所嘲笑的内容。

演示：

>>> 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