[英]Error while testing the raise of self-defined exceptions (using assertRaises())
[英]using assertRaises - handling propagated exceptions
我有一些代码正在测试包装的异常,当它失败并且异常传播时,我认为错误消息和追溯信息不够详细,主要是因为它没有告诉我与测试相比预期的结果,我想了解例外情况和期望的详细信息。
我调整了测试(请参见下面的示例代码)。 我想知道这种方法是否有效,是否有任何Python测试或模拟框架可以直接实现? (当前我正在使用unittest和mox)
该问题的答案之一简单地涉及了在这种情况下使用self.fail的适当性,但并未详细说明。 我的假设是,如果我尝试将测试限制在一个区域,则可以通过测试。
注意:如果您运行该代码示例,该示例将失败,以演示我希望看到的行为。 我正在使用Python 2.7,Mox 0.5.3
import sys
import urllib2
from contextlib import closing
try:
import lxml.etree as ET
except ImportError:
import xml.etree.ElementTree as ET
class Defect(Exception):
"""Wrapped exception, for module error detection"""
def __init__(self, *args):
Exception.__init__(self, *args)
self.wrapped_exc = sys.exc_info()
class StudioResources:
"""Dummy class"""
def _opener(self, request, html=False):
with closing(urllib2.urlopen(request)) as response:
try:
if html:
import lxml.html
return lxml.html.parse(response)
else:
return ET.parse(response)
except urllib2.HTTPError, e:
if e.code in [400, 500]: # Bad Request, Internal Server Error
raise Defect, "report error to the library maintainer"
else:
raise
###
# Tests
###
import unittest
import mox
import traceback
import difflib
import urllib
import httplib
def format_expectation(exc_expected=None, exc_instance=None):
"""Synopsis - For exceptions, inspired by _AssertRaisesContext
try:
self.assertRaises(myexc, self.studio._opener, None)
except Exception, e:
self.fail(format_expectation(exc_expected=myexc, exc_instance=e))
"""
if not isinstance(exc_expected, type) or exc_instance is None:
raise ValueError, "check __init__ args"
differ = difflib.Differ()
inst_class = exc_instance.__class__
def fullname(c): return "%s.%s" % (c.__module__, c.__name__)
diff = differ.compare(
(fullname(inst_class),), (fullname(exc_expected),))
_str = ("Unexpected Exception type. unexpected:- expected:+\n%s"
% ("\n".join(diff),))
return _str
class StudioTest(mox.MoxTestBase):
def setUp(self):
mox.MoxTestBase.setUp(self)
self.studio = StudioResources()
def test_opener_defect(self):
f = urllib.addinfourl(urllib2.StringIO('dummy'), None, None)
RESP_CODE = 501
self.mox.StubOutWithMock(f, 'read')
self.mox.StubOutWithMock(urllib2, 'urlopen')
urllib2.urlopen(mox.IgnoreArg()).AndReturn(f)
f.read(mox.IgnoreArg()).AndRaise(urllib2.HTTPError(
'http://c.com', RESP_CODE, httplib.responses[RESP_CODE], "", None))
self.mox.ReplayAll()
try:
with self.assertRaises(Defect) as exc_info:
self.studio._opener(None)
except Exception, e:
traceback.print_exc()
self.fail(format_expectation(exc_expected=Defect, exc_instance=e))
# check the response code
exc, inst, tb = exc_info.exception.wrapped_exc
self.assertEquals(inst.code, RESP_CODE)
self.mox.VerifyAll()
if __name__ == '__main__':
unittest.main()
在编写单元测试时,将测试限制为一件事总是一个好主意。 我看不到您的代码有什么问题,但我会将所有内容包装在上下文管理器中。 我使用鼻子而不是unittest,它将任何AssertionError都视为失败(这意味着不需要调用self.fail()
),并且我编写了自己的上下文管理器来处理这种情况。 如果您有兴趣,请参见以下代码:
class assert_raises:
def __init__(self, exception):
self.exception = exception
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
assert exc_type is self.exception, "Got '{}', expected '{}'"\
.format('None' if exc_type is None else exc_type.__name__,
self.exception.__name__)
return True
然后如以下示例所示使用它:
>>> with assert_raised(ValueError):
... raise ValueError
>>> with assert_raised(ValueError):
... pass
Traceback (most recent call last):
...
AssertionError: Got 'None', expected 'ValueError'
>>> with assert_raised(ValueError):
... raise TypeError
Traceback (most recent call last):
...
AssertionError: Got 'TypeError', expected 'ValueError'
由于引发了AssertionError,鼻子将其视为失败,并且无论如何都会打印完整的回溯。 这是为鼻子设计的,但是要针对单元测试和mox进行调整将是一件微不足道的事情。 如果您不太担心故障的确切模式,您甚至可以按原样使用它。
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