Python：模拟上下文管理器
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Python: Mocking a context manager
提问by Willem
I don't understand why I can't mock NamedTemporaryFile.name in this example:
我不明白为什么我不能在这个例子中模拟 NamedTemporaryFile.name ：
from mock import Mock, patch
import unittest
import tempfile
def myfunc():
with tempfile.NamedTemporaryFile() as mytmp:
return mytmp.name
class TestMock(unittest.TestCase):
@patch('tempfile.NamedTemporaryFile')
def test_cm(self, mock_tmp):
mytmpname = 'abcde'
mock_tmp.__enter__.return_value.name = mytmpname
self.assertEqual(myfunc(), mytmpname)
Test results in:
测试结果：
AssertionError: <MagicMock name='NamedTemporaryFile().__enter__().name' id='140275675011280'> != 'abcde'
采纳答案by Michele d'Amico
You are setting the wrong mock: mock_tmpis not the context manager, but instead returnsa context manager. Replace your setup line with:
您设置了错误的模拟：mock_tmp不是上下文管理器，而是返回一个上下文管理器。将您的设置行替换为：
mock_tmp.return_value.__enter__.return_value.name = mytmpname
and your test will work.
并且您的测试将起作用。
回答by Peter K
Here is an alternative with pytestand mocker fixture, which is a common practice as well:
这是pytest和mocker fixture的替代方案，这也是一种常见做法：
def test_myfunc(mocker):
mock_tempfile = mocker.MagicMock(name='tempfile')
mocker.patch(__name__ + '.tempfile', new=mock_tempfile)
mytmpname = 'abcde'
mock_tempfile.NamedTemporaryFile.return_value.__enter__.return_value.name = mytmpname
assert myfunc() == mytmpname
回答by hmobrienv
Extending Peter K's answer using pytest and the mocker fixture.
使用 pytest 和模拟装置扩展 Peter K 的答案。
def myfunc():
with tempfile.NamedTemporaryFile(prefix='fileprefix') as fh:
return fh.name
def test_myfunc(mocker):
mocker.patch('tempfile.NamedTemporaryFile').return_value.__enter__.return_value.name = 'tempfilename'
assert myfunc() == 'tempfilename'
