@mock.patch 即使在设置side_effect后也不会引发属性错误

Question

我正在尝试修复python包caniusepython3中的一个错误，该错误是由于distlib没有正确解析pypi项目而出现的。我已经写了这个单元测试

 @mock.patch('distlib.locators.locate')
 def test_blocking_dependencies_locators_fails(self, distlib_mock):
     """
     Testing the work around for //bitbucket.org/pypa/distlib/issue/59/
     """
     py3 = {'py3_project': ''}
     breaking_project = 'test_project'
     distlib_mock.locators.locate.return_value = "foo"
     distlib_mock.locators.locate.side_effect = AttributeError()
     got = dependencies.blocking_dependencies([breaking_project], py3)
     # If you'd like to test that a message is logged we can use 
     # testfixtures.LogCapture or stdout redirects.

因此，当 distlib 在下一个版本的 distlib 中修复错误时，测试用例仍然有效。

问题是 MagicMock 永远不会像我预期的那样引发 AttributeError，而是返回魔术模拟对象的字符串表示形式

try:
    # sets dist to <MagicMock name='locate()' id='4447530792'>
    dist = distlib.locators.locate(project)
except AttributeError:
    # This is a work around //bitbucket.org/pypa/distlib/issue/59/
    log.warning('{0} found but had to be skipped.'.format(project))
    continue

并导致稍后出现此堆栈跟踪，因为它返回对象 repr，

======================================================================
ERROR: Testing the work around for //bitbucket.org/pypa/distlib/issue/59/
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/Cellar/python3/3.4.2_1/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/mock.py", line 1136, in patched
    return func(*args, **keywargs)
  File "/Users/alexlord/git/caniusepython3/caniusepython3/test/test_dependencies.py", line 81, in test_blocking_dependencies_locators_fails
    got = dependencies.blocking_dependencies([breaking_project], py3)
  File "/Users/alexlord/git/caniusepython3/caniusepython3/dependencies.py", line 119, in blocking_dependencies
    return reasons_to_paths(reasons)
  File "/Users/alexlord/git/caniusepython3/caniusepython3/dependencies.py", line 43, in reasons_to_paths
    parent = reasons[blocker]
  File "/Users/alexlord/git/caniusepython3/caniusepython3/dependencies.py", line 29, in __getitem__
    return super(LowerDict, self).__getitem__(key.lower())
nose.proxy.KeyError: <MagicMock name='locate().name.lower().lower()' id='4345929400'>
-------------------- >> begin captured logging << --------------------
ciu: INFO: Checking top-level project: test_project ...
ciu: INFO: Locating <MagicMock name='locate().name.lower()' id='4344734944'>
ciu: INFO: Dependencies of <MagicMock name='locate().name.lower()' id='4344734944'>: []
--------------------- >> end captured logging << ---------------------

为什么 MagicMock 在调用 distlib.locator.locate() 时不返回异常？

更新：当我切换到使用

def test_blocking_dependencies_locators_fails(self):
    """
    Testing the work around for //bitbucket.org/pypa/distlib/issue/59/
    """
    with mock.patch.object(distlib.locators, 'locate') as locate_mock:
        py3 = {'py3_project': ''}
        breaking_project = 'test_project'
        locate_mock.side_effect = AttributeError()
        got = dependencies.blocking_dependencies([breaking_project], py3)
        # If you'd like to test that a message is logged we can use 
        # testfixtures.LogCapture or stdout redirects.

但我仍然想知道我在装饰器格式上做错了什么。

Answer 1

当你使用 @mock.patch 时，它会模拟你告诉它的内容，并将该模拟对象作为参数传递。因此，您的distlib_mock参数是模拟locate函数。您实际上是在distlib.locators.locate.locators.locate 上设置属性。直接在提供的模拟上设置属性，事情应该会更好。

@mock.patch('distlib.locators.locate')
def test_blocking_dependencies_locators_fails(self, locate_mock):
    # ...
    locate_mock.return_value = "foo"
    locate_mock.side_effect = AttributeError()
    # ...