Python unittest模拟:是否可以在测试时模拟方法的默认参数的值? [英] Python unittest mock: Is it possible to mock the value of a method's default arguments at test time?

问题描述

我有一个接受默认参数的方法:

I have a method that accepts default arguments:

def build_url(endpoint, host=settings.DEFAULT_HOST):
    return '{}{}'.format(host, endpoint)

我有一个使用此方法的测试用例:

I have a test case that exercises this method:

class BuildUrlTestCase(TestCase):
    def test_build_url(self):
        """ If host and endpoint are supplied result should be 'host/endpoint' """

        result = build_url('/end', 'host')
        expected = 'host/end'

        self.assertEqual(result,expected)

     @patch('myapp.settings')
     def test_build_url_with_default(self, mock_settings):
        """ If only endpoint is supplied should default to settings"""
        mock_settings.DEFAULT_HOST = 'domain'

        result = build_url('/end')
        expected = 'domain/end'

        self.assertEqual(result,expected)

如果我将调试点放在build_url中并检查此属性，则settings.DEFAULT_HOST返回模拟值.但是，测试继续失败，并且断言指示host被分配了我实际的settings.py中的值.我知道这是因为host关键字参数是在导入时设置的，并且未考虑我的模拟.

If I drop a debug point in build_url and inspect this attribute settings.DEFAULT_HOST returns the mocked value. However the test continues to fail and the assertion indicates host is assigned the value from my actual settings.py. I know this is because the host keyword argument is set at import time and my mock is not considered.

调试器

(Pdb) settings
<MagicMock name='settings' id='85761744'>                                                                                                                                                                                               
(Pdb) settings.DEFAULT_HOST
'domain'
(Pdb) host
'host-from-settings.com'                                                                                                                                                 

是否可以在测试时覆盖此值，以便可以使用模拟的settings对象行使默认路径?

Is there a way to override this value at test time so that I can exercise the default path with a mocked settings object?

推荐答案

定义函数后，函数会将其参数默认值存储在func_defaults属性中，因此您可以对其进行修补.像

Functions store their parameter default values in the func_defaults attribute when the function is defined, so you can patch that. Something like

def test_build_url(self):
    """ If only endpoint is supplied should default to settings"""

    # Use `func_defaults` in Python2.x and `__defaults__` in Python3.x.
    with patch.object(build_url, 'func_defaults', ('domain',)):
      result = build_url('/end')
      expected = 'domain/end'

    self.assertEqual(result,expected)

我使用patch.object作为上下文管理器而不是装饰器，以避免不必要的补丁对象作为参数传递给test_build_url.

I use patch.object as a context manager rather than a decorator to avoid the unnecessary patch object being passed as an argument to test_build_url.

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