在python中模拟文件对象或可迭代对象 [英] Mocking file objects or iterables in python

问题描述

哪种方法适合模拟和测试由 open()返回的iters对象的代码，使用 mock 库?

Which way is proper for mocking and testing code that iters object returned by open(), using mock library?

whitelist_data.py:

WHITELIST_FILE = "testdata.txt"

format_str = lambda s: s.rstrip().lstrip('www.')
whitelist = None

with open(WHITELIST_FILE) as whitelist_data:
    whitelist = set(format_str(line) for line in whitelist_data)

if not whitelist:
    raise RuntimeError("Can't read data from %s file" % WHITELIST_FILE)

def is_whitelisted(substr):
    return 1 if format_str(substr) in whitelist else 0

这是我尝试进行测试的方式.

Here's how I try to test it.

import unittest
import mock 

TEST_DATA = """
domain1.com
domain2.com
domain3.com
"""

class TestCheckerFunctions(unittest.TestCase):

    def test_is_whitelisted_method(self):
        open_mock = mock.MagicMock()
        with mock.patch('__builtin__.open',open_mock):
            manager = open_mock.return_value.__enter__.return_value
            manager.__iter__ = lambda s: iter(TEST_DATA.splitlines())
            from whitelist_data import is_whitelisted
            self.assertTrue(is_whitelisted('domain1.com'))

if __name__ == '__main__':
    unittest.main()

python tests.py的结果是:

$ python tests.py

E
======================================================================
ERROR: test_is_whitelisted_method (__main__.TestCheckerFunctions)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests.py", line 39, in test_is_whitelisted_method
    from whitelist_data import is_whitelisted
  File "/Users/supa/Devel/python/whitelist/whitelist_data.py", line 20, in <module>
    whitelist = set(format_str(line) for line in whitelist_data)
TypeError: 'Mock' object is not iterable

----------------------------------------------------------------------
Ran 1 test in 0.001s

UPD::由于Adam，我重新安装了模拟库(pip install -e hg+https://code.google.com/p/mock#egg=mock)并更新了tests.py.就像魅力一样.

UPD: Thanks to Adam, I've reinstalled mock library(pip install -e hg+https://code.google.com/p/mock#egg=mock) and updated tests.py. Works like a charm.

推荐答案

您正在寻找MagicMock.这支持迭代.

You're looking for a MagicMock. This supports iteration.

在模拟0.80beta4中，patch返回MagicMock.因此，这个简单的示例有效:

In mock 0.80beta4, patch returns a MagicMock. So this simple example works:

import mock

def foo():
    for line in open('myfile'):
        print line

@mock.patch('__builtin__.open')
def test_foo(open_mock):
    foo()
    assert open_mock.called

如果您正在运行模拟0.7.x(看起来像您一样)，我认为您不能仅使用补丁来完成此任务.您需要分别创建模拟，然后将其传递到补丁中:

If you're running mock 0.7.x (It looks like you are), I don't think you can accomplish this with patch alone. You'll need to create the mock separately, then pass it into patch:

import mock

def foo():
    for line in open('myfile'):
        print line

def test_foo():
    open_mock = mock.MagicMock()
    with mock.patch('__builtin__.open', open_mock):
        foo()
        assert open_mock.called

---

注意-我已经使用py.test运行了这些，但是，这些相同的方法也可以用于unittest.

---

Note - I've run these with py.test, however, these same approaches will work with unittest as well.

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