当 python 模拟同时具有返回值和副作用列表时会发生什么? [英] What happens when a python mock has both a return value and a list of side effects?

问题描述

我无法理解某些测试代码中发生的情况.它看起来像这样:

导入pytest从 unittest.mock 导入 MagicMock从 my_module 导入 MyClass混淆模拟 = MagicMock(return_value=b"",副作用=[连接错误()，b"another_return_value?",b"another_another_return_value?"])mocked_class = MyClass()monkeypatch.setattr(模拟类，method_to_call_thrice"，混淆模拟)

我知道:

• side_effect 是在调用模拟时调用的函数
• 但是如果 side_effect 是可迭代的，那么对模拟的每次调用都会从迭代中返回下一个值"(感谢 pytest文档)
• 文档还说，如果函数传递给 side_effect返回 DEFAULT，然后模拟将从中返回它的正常值return_value

但这是我没有得到的:

• 当我提供同时一个副作用列表和一个返回值?
• 每次调用 MyClass.method_to_call_thrice 时我应该看到什么?

解决方案

side_effect 被使用.列表值可以包含mock.DEFAULT，函数可以返回mock.DEFAULT，表示使用return_value属性的值.

<预><代码>>>>导入 unittest.mock>>>m = unittest.mock.Mock(return_value="foo",... side_effect=[1, 2, unittest.mock.DEFAULT, 4, 5])>>>米()1>>>米()2>>>米()'富'>>>米()4>>>米()5>>>unittest.mock.Mock(return_value="foo",... side_effect=lambda: unittest.mock.DEFAULT)()'富'

I'm having trouble understanding what's happening in some test code. It looks like this:

import pytest
from unittest.mock import MagicMock
from my_module import MyClass

confusing_mock = MagicMock(
    return_value=b"",
    side_effect=[
        ConnectionError(),
        b"another_return_value?",
        b"another_another_return_value?"
    ])

mocked_class = MyClass()
monkeypatch.setattr(mocked_class, "method_to_call_thrice", confusing_mock)

I know that:

• side_effect is a function to be called whenever the mock is called
• but if side_effect is an iterable, then "each call to the mock will return the next value from the iterable" (thanks pytest docs)
• the docs also say that if the function passed to side_effect returns DEFAULT, then the mock will return it's normal value from return_value

But here's what I don't get:

• What happens when I provide both a list of side effects and a return value?
• What should I expect to see on each call of MyClass.method_to_call_thrice?

解决方案

side_effect is used. A list value can contain mock.DEFAULT, and a function can return mock.DEFAULT, to indicate that the value of the return_value attribute be used.

>>> import unittest.mock
>>> m = unittest.mock.Mock(return_value="foo",
...                        side_effect=[1, 2, unittest.mock.DEFAULT, 4, 5])
>>> m()
1
>>> m()
2
>>> m()
'foo'
>>> m()
4
>>> m()
5
>>> unittest.mock.Mock(return_value="foo",
...                    side_effect=lambda: unittest.mock.DEFAULT)()
'foo'

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