Python模拟基类的属性 [英] Python mock a base class's attribute

问题描述

为了进行测试，我想在基类中更改单个Class实例的属性(self.attr).

For testing, I'd like to change a single Class instance's attribute (self.attr) in a base class.

# app.py
class Base():
    def __init__(self):
        self.attr = 'original_value'

    def show(self):
        print(self.attr) 

class App():
    def __init__(self):  
        self.base = Base()

这是我尝试模拟基类实例的属性attr

Here is my attempt at mocking the Base class instance's attribute attr

# test_app.py
from mock import Mock
from app import App

def test_mock_inherited_class_instance():
    """ With mocking. Change app.base.attr from 'original_value' to 'new_value'.
    """
    app = App()
    app.base = Mock()
    app.base.attr = 'new_value'
    app.base.show() # I'd like this to show 'new_value', NOT 'original_value'

推荐答案

类的实例成员或实例变量与类属性或类属性不同.只能通过保留所有类属性来嘲笑attr.

The instance member or instance variable of a class is different from class attribute or class property. this mocked the attr only by keeping all class attributes.

import mock
from app import App
from app import Base
import unittest
from StringIO import StringIO
class TestApp(unittest.TestCase):

    @mock.patch('sys.stdout', new_callable=StringIO)
    def test_mock_instance_var(self, mocked_stdout):

        base = Base()
        app = App()

        mock_base = mock.MagicMock(name='Base', spec=Base)
        instance = mock_base.return_value
        instance.attr.return_value = 'mmm'
        base.attr = instance.attr.return_value
        self.assertEqual(base.attr, 'mmm')

        app.base = base

        self.assertEqual(app.base.attr, 'mmm')
        # the print stdout of show()
        app.base.show()
        self.assertEqual(mocked_stdout.getvalue(), 'mmm\n')

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