模拟函数引发异常以测试except块 [英] Mocking a function to raise an Exception to test an except block
问题描述
我有一个函数(foo)，该函数调用了另一个函数(bar).如果调用bar()会引发一个HttpError，则我想特别处理状态代码为404的情况，否则请重新引发.
I have a function (foo) which calls another function (bar). If invoking bar() raises an HttpError, I want to handle it specially if the status code is 404, otherwise re-raise.
我正在尝试围绕此foo函数编写一些单元测试，以模拟对bar()的调用.不幸的是，我无法对bar()进行模拟调用以引发被我的except块捕获的异常.
I am trying to write some unit tests around this foo function, mocking out the call to bar(). Unfortunately, I am unable to get the mocked call to bar() to raise an Exception which is caught by my except block.
这是说明我问题的代码:
Here is my code which illustrates my problem:
import unittest
import mock
from apiclient.errors import HttpError
class FooTests(unittest.TestCase):
@mock.patch('my_tests.bar')
def test_foo_shouldReturnResultOfBar_whenBarSucceeds(self, barMock):
barMock.return_value = True
result = foo()
self.assertTrue(result) # passes
@mock.patch('my_tests.bar')
def test_foo_shouldReturnNone_whenBarRaiseHttpError404(self, barMock):
barMock.side_effect = HttpError(mock.Mock(return_value={'status': 404}), 'not found')
result = foo()
self.assertIsNone(result) # fails, test raises HttpError
@mock.patch('my_tests.bar')
def test_foo_shouldRaiseHttpError_whenBarRaiseHttpErrorNot404(self, barMock):
barMock.side_effect = HttpError(mock.Mock(return_value={'status': 500}), 'error')
with self.assertRaises(HttpError): # passes
foo()
def foo():
try:
result = bar()
return result
except HttpError as error:
if error.resp.status == 404:
print '404 - %s' % error.message
return None
raise
def bar():
raise NotImplementedError()
我遵循了模拟文档，其中说:您应该将Mock实例的side_effect设置为Exception类，以使模拟函数引发错误.
I followed the Mock docs which say that you should set the side_effect of a Mock instance to an Exception class to have the mocked function raise the error.
我还查看了其他一些相关的StackOverflow Q& A，看来我正在做他们正在做的相同事情，以使他们的模拟引发异常.
I also looked at some other related StackOverflow Q&As, and it looks like I am doing the same thing they are doing to cause and Exception to be raised by their mock.
- https://stackoverflow.com/a/10310532/346561
- How to use Python Mock to raise an exception - but with Errno set to a given value
为什么设置barMock的side_effect不会导致预期的Exception升高?如果我做的事情很奇怪，应该如何在except块中测试逻辑?
Why is setting the side_effect of barMock not causing the expected Exception to be raised? If I am doing something weird, how should I go about testing logic in my except block?
推荐答案
您的模拟正在引发异常，但是error.resp.status值丢失了.而不是使用return_value，只需告诉Mock status是属性:
Your mock is raising the exception just fine, but the error.resp.status value is missing. Rather than use return_value, just tell Mock that status is an attribute:
barMock.side_effect = HttpError(mock.Mock(status=404), 'not found')
Mock()的其他关键字参数设置为结果对象的属性.
Additional keyword arguments to Mock() are set as attributes on the resulting object.
我将您的foo和bar定义放在my_tests模块中/googleapiclient/errors.py#L35-L63"rel =" noreferrer> HttpError类，这样我也可以使用它，然后您的测试就可以成功运行:
I put your foo and bar definitions in a my_tests module, added in the HttpError class so I could use it too, and your test then can be ran to success:
>>> from my_tests import foo, HttpError
>>> import mock
>>> with mock.patch('my_tests.bar') as barMock:
... barMock.side_effect = HttpError(mock.Mock(status=404), 'not found')
... result = my_test.foo()
...
404 -
>>> result is None
True
您甚至可以看到print '404 - %s' % error.message行，但是我想您想在那里使用error.content；这就是HttpError()从第二个参数开始设置的属性，无论如何.
You can even see the print '404 - %s' % error.message line run, but I think you wanted to use error.content there instead; that's the attribute HttpError() sets from the second argument, at any rate.
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