Question

我需要测试一个需要使用urllib.urlopen在外部服务器上查询页面的函数（它还使用urllib.urlencode）。服务器可能已关闭，页面可能会更改;我不能依赖它进行测试。

控制urllib.urlopen返回的最佳方法是什么？

Answer 1

另一个简单的方法是让你的测试覆盖urllib的urlopen()函数。例如，如果您的模块有

import urllib

def some_function_that_uses_urllib():
    ...
    urllib.urlopen()
    ...

您可以像这样定义测试：

import mymodule

def dummy_urlopen(url):
    ...

mymodule.urllib.urlopen = dummy_urlopen

然后，当您的测试调用mymodule中的函数时，将调用dummy_urlopen()而不是真实urlopen()。像Python这样的动态语言可以非常容易地删除用于测试的方法和类。

请参阅http://softwarecorner.wordpress.com/上的博客文章，了解有关存根测试依赖关系的更多信息。

Answer 2

我正在使用Mock's补丁修饰符：

from mock import patch

[...]

@patch('urllib.urlopen')
def test_foo(self, urlopen_mock):
    urlopen_mock.return_value = MyUrlOpenMock()

Answer 3

你看过Mox了吗？它应该做你需要的一切。这是一个简单的交互式会话，说明您需要的解决方案：

>>> import urllib
>>> # check that it works
>>> urllib.urlopen('http://www.google.com/')
<addinfourl at 3082723820L ...>
>>> # check what happens when it doesn't
>>> urllib.urlopen('http://hopefully.doesnotexist.com/')
#-- snip --
IOError: [Errno socket error] (-2, 'Name or service not known')

>>> # OK, let's mock it up
>>> import mox
>>> m = mox.Mox()
>>> m.StubOutWithMock(urllib, 'urlopen')
>>> # We can be verbose if we want to :)
>>> urllib.urlopen(mox.IgnoreArg()).AndRaise(
...   IOError('socket error', (-2, 'Name or service not known')))

>>> # Let's check if it works
>>> m.ReplayAll()
>>> urllib.urlopen('http://www.google.com/')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.5/site-packages/mox.py", line 568, in __call__
    raise expected_method._exception
IOError: [Errno socket error] (-2, 'Name or service not known')

>>> # yay! now unset everything
>>> m.UnsetStubs()
>>> m.VerifyAll()
>>> # and check that it still works
>>> urllib.urlopen('http://www.google.com/')
<addinfourl at 3076773548L ...>

Answer 4

HTTPretty的工作方式与FakeWeb完全相同。 HTTPretty在套接字层中工作，因此它应该可以拦截任何python http客户端库。它针对urllib2，httplib2和请求

进行了战斗测试

import urllib2
from httpretty import HTTPretty, httprettified


@httprettified
def test_one():
    HTTPretty.register_uri(HTTPretty.GET, "http://yipit.com/",
                           body="Find the best daily deals")

    fd = urllib2.urlopen('http://yipit.com')
    got = fd.read()
    fd.close()

    assert got == "Find the best daily deals"

Answer 5

处理此问题的最佳方法可能是拆分代码，以便处理页面内容的逻辑从提取页面的代码中分离出来。

然后将fetcher代码的实例传递给处理逻辑，然后您可以使用模拟提取器轻松替换它以进行单元测试。

e.g。

class Processor(oject):
    def __init__(self, fetcher):
        self.m_fetcher = fetcher

    def doProcessing(self):
        ## use self.m_fetcher to get page contents

class RealFetcher(object):
    def fetchPage(self, url):
        ## get real contents

class FakeFetcher(object):
    def fetchPage(self, url):
        ## Return whatever fake contents are required for this test

Answer 6

如果您不想加载模块：

import sys,types
class MockCallable():
  """ Mocks a function, can be enquired on how many calls it received """
  def __init__(self, result):
    self.result  = result
    self._calls  = []

  def __call__(self, *arguments):
    """Mock callable"""
    self._calls.append(arguments)
    return self.result

  def called(self):
    """docstring for called"""
    return self._calls

class StubModule(types.ModuleType, object):
  """ Uses a stub instead of loading libraries """

  def __init__(self, moduleName):
    self.__name__ = moduleName
    sys.modules[moduleName] = self

  def __repr__(self):
    name  = self.__name__
    mocks = ', '.join(set(dir(self)) - set(['__name__']))
    return "<StubModule: %(name)s; mocks: %(mocks)s>" % locals()

class StubObject(object):
  pass

然后：

>>> urllib = StubModule("urllib")
>>> import urllib # won't actually load urllib

>>> urls.urlopen = MockCallable(StubObject())

>>> example = urllib.urlopen('http://example.com')
>>> example.read = MockCallable('foo')

>>> print(example.read())
'foo'

Answer 7

最简单的方法是更改函数，使其不一定使用urllib.urlopen。让我们说这是你原来的功能：

def my_grabber(arg1, arg2, arg3):
    # .. do some stuff ..
    url = make_url_somehow()
    data = urllib.urlopen(url)
    # .. do something with data ..
    return answer

添加一个参数，该参数是用于打开URL的函数。然后你可以提供一个模拟函数来做你需要的任何事情：

def my_grabber(arg1, arg2, arg3, urlopen=urllib.urlopen):
    # .. do some stuff ..
    url = make_url_somehow()
    data = urlopen(url)
    # .. do something with data ..
    return answer

def test_my_grabber():
    my_grabber(arg1, arg2, arg3, urlopen=my_mock_open)

Answer 8

添加到克林特·米勒（Clint Miller）的答案上，要做到这一点，我必须创建一个伪类，该类实现如下所示的read方法：

class FakeURL:
    def read(foo):
        return '{"some":"json_text"}'

然后将urllib2.open存根：

# Stub out urllib2.open.
def dummy_urlopen(foo, bar, baz):
  return FakeURL()
urllib2.urlopen = dummy_urlopen

一个mock / stub python模块如何像urllib一样

8 个答案: