五夜光寒，照来积雪平于栈。西风何限，自起披衣看。
对此茫茫，不觉成长叹。何时旦，晓星欲散，飞起平沙雁。

在某个Python程序中看到这么一行

from unittest import mock

看起来像是一个Python自带的测试库。经查，unittest.mock允许用户使用假的对象代替系统的真实对象。mock库中常用的是MagicMock, Mock, patch()：

>>> from unittest.mock import MagicMock
>>> thing = ProductionClass()
>>> thing.method = MagicMock(return_value=3)
>>> thing.method(3, 4, 5, key='value')
3

可以看出MagicMock可以改变函数为固定输出。同事可以使用side_effect参数使得函数具有其他功能，可以实现函数的功能或者报错。

>>> mock = Mock(side_effect=KeyError('foo'))
>>> mock()
Traceback (most recent call last):
 ...
KeyError: 'foo'

>>> values = {'a': 1, 'b': 2, 'c': 3}
>>> def side_effect(arg):
...     return values[arg]
...
>>> mock.side_effect = side_effect
>>> mock('a'), mock('b'), mock('c')
(1, 2, 3)
>>> mock.side_effect = [5, 4, 3, 2, 1]
>>> mock(), mock(), mock()
(5, 4, 3)

利用patch()装饰器可以声明一个测试环境下的类或对象。（到这里我才想到去查一查mock的意思）

A mock object is a dummy implementation for an interface or a class in which you define the output of certain method calls. Mock objects are configured to perform a certain behavior during a test. They typically record the interaction with the system and tests can validate that.

另：在这段程序中mock的用法是给host程序传参一个虚假的对象

Applicaiton.register_service(mock.Mock())

NAME

unittest

MODULE REFERENCE

https://docs.python.org/3.7/library/unittest

DESCRIPTION

Python unit testing framework.

import unittest

class InterArithmeticTestCase(unittest.TestCase):
    def testAdd(self): # test method names begin with 'test'
        self.assertEqual((1+2), 3)
        self.assertEqual((0+1), 1)

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