python - 如何正确模拟类(class)的私有(private)成员

Question

我正在尝试为依赖于另一个私有(private)方法的方法编写一些单元测试。 - 如下例所示:

def is_member_of(self, group_name):
  members = self.__get_group_members(group_name)

我想模拟的私有(private)方法是__get_group_members；我还想模拟私有(private)属性 __user_id，因为它将在 is_member_of 函数中使用(上例中未显示)。

我目前拥有的:

import unittest
from unittest import mock

class Test(unittest.TestCase):
  group_data = []
  user_id = 'test_user_id'

  def mock_dependencies(self, x):
    x.__user_id = mock.PropertyMock(return_value=self.user_id)
    x.__get_group_members = mock.MagicMock(return_value=self.group_data)

  def first_test(self):
    x = A(('name', 'group'))
    self.mock_dependencies(x)
    x.is_member_of('test_group')

当我调用 x.is_member_of() 时，模拟无法按预期工作。

Answer 1

您可以在 Python 中访问私有(private)属性，因为 private 和 protected 是约定俗成的。 - 您正在寻找的基本上是使用 _ClassName__private_attribute_name，因为 python 执行重命名以实现约定的公约。

示例(返回 MagicMock):

with mock.patch.object(Class, '_ClassName__private_attribute_name', return_value='value') as obj_mock:
    pass

示例(返回原始值):

with mock.patch.object(Class, '_ClassName__private_attribute_name', new_callable=PropertyMock) as obj_mock:
    obj_mock.return_value = 'string value'

Class 是对类本身的引用 - 而不是实例。

完整示例:

from unittest.mock import patch, PropertyMock
from unittest import TestCase, main


class Private:
    __attr = 'hello'


class PrivateTest(TestCase):
    @patch.object(Private, '_Private__attr', new_callable=PropertyMock)
    def test_private_attribute_value_change_decorator_success(self, private_mock):
        obj = Private()
        private_mock.return_value = 'string'

        self.assertEqual('string', obj._Private__attr)

    def test_private_attribute_value_change_context_manager_success(self):
        with patch.object(Private, '_Private__attr', new_callable=PropertyMock) as o_mock:
            obj = Private()

            o_mock.return_value = 'mocked value'
            self.assertEqual('mocked value', obj._Private__attr)


if __name__ == '__main__':
    main()

对示例的修改:

from unittest import TestCase, mock, main


class A:
    __user_id = 3

    def __init__(self, user, group):
        """
        Your logic is missing - obviously
        :param user:
        :param group:
        """


    def __get_group_members(self):
        """
        Your logic is missing - obviously
        :return:
        """
        return ['user_1', 'user_2']

    def is_member_of(self, group_name):
        members = self.__get_group_members(group_name)

        # will return if the user is a member of the group
        return self.__user_id in members


class GroupTest(TestCase):
    group_data = [1, 2]
    user_id = 'test_user_id'

    @mock.patch.object(A, '_A__get_group_members')
    @mock.patch.object(A, '_A__user_id', new_callable=mock.PropertyMock)
    def test_this_is_my_first_success(self, user_id_mock: mock.PropertyMock, get_group_members_mock: mock.MagicMock):
        get_group_members_mock.return_value = self.group_data
        user_id_mock.return_value = 3

        x = A('user_3', 'this_group')
        self.assertEqual(False, x.is_member_of('test_group'))

    @mock.patch.object(A, '_A__get_group_members')
    @mock.patch.object(A, '_A__user_id', new_callable=mock.PropertyMock)
    def test_this_is_my_first_failure(self, user_id_mock: mock.PropertyMock, get_group_members_mock: mock.MagicMock):
        get_group_members_mock.return_value = self.group_data
        user_id_mock.return_value = 1

        x = A('user_1', 'this_group')
        self.assertEqual(True, x.is_member_of('test_group'))


if __name__ == '__main__':
    main()

如果您知道您将在所有测试用例中模拟这两个属性，您可以在类级别添加装饰器并期待类似的参数。

如果属性是通过 __init__ 或任何其他方法设置的，您可以简单地更改它，如下所示。

from unittest import TestCase, mock, main


class A:
    def __init__(self, user, group):
        """
        Your logic is missing - obviously
        :param user:
        :param group:
        """


    def __get_group_members(self):
        """
        Your logic is missing - obviously
        :return:
        """
        return ['user_1', 'user_2']

    def is_member_of(self, group_name):
        members = self.__get_group_members(group_name)

        # will return if the user is a member of the group
        return self.__user_id in members


class GroupTest(TestCase):
    group_data = [1, 2]
    user_id = 'test_user_id'

    @mock.patch.object(A, '_A__get_group_members')
    def test_this_is_my_first_success(self, get_group_members_mock: mock.MagicMock):
        x = A('user_3', 'this_group')

        x._A__user_id = 5
        get_group_members_mock.return_value = self.group_data

        self.assertEqual(False, x.is_member_of('test_group'))

    @mock.patch.object(A, '_A__get_group_members')
    def test_this_is_my_first_failure(self, get_group_members_mock: mock.MagicMock):
        get_group_members_mock.return_value = self.group_data

        x = A('user_1', 'this_group')
        x._A__user_id = 1
        self.assertEqual(True, x.is_member_of('test_group'))


if __name__ == '__main__':
    main()