python - 如何恢复模拟

Question

当我弄清楚为什么我的测试文件运行顺利但如果测试与 pytest 一起为整个包运行时中断，我几乎要发疯了。 .
我有一个父类和一个子类。 child 调用 parent 的 init 如下:

class Child(Parent):
    __init__(...,**kwargs):
        ...
        super().__init__(**kwargs)

我想通过一个小测试来定义这种行为。

from unittest.mock import Mock

def test_init_calls_parent_init():
    Parent.__init__ = Mock()
    
    Child()

    assert Parent.__init__.called

问题是 Parent.__init__ 始终保持模拟对于其他文件中的所有以下测试。
我的想法是把它放到一个函数作用域中使它只是一个临时的改变。当然，由于这些测试失败了，它们隐含地定义了对父级 init 的需求，但我也想确保使用一个显式测试。
我应该创建一些 pytest设置/拆卸或防止这种情况的公认方法是什么？

Answer 1

当你执行 Parent.__init__ = Mock() ，你基本上重新定义了__init__模块本身，然后反射(reflect)在随后的测试中。
而不是手动更改 Parent.__init__ 的实现至Mock ，我的建议是改用 unittest 中已有的修补功能。和 pytest-mock .

我们也可以使用monkeypatch正如@MattSom 所建议的(见评论部分)

src.py

class Parent:
    def __init__(self, **kwargs):
        print("Parent __init__ called")

class Child(Parent):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        print("Child __init__ called")

没有更正:

from unittest.mock import Mock, patch

from src import Child, Parent


def test_init_calls_real_parent_init():
    Child()


def test_init_calls_updated_parent_init():
    Parent.__init__ = Mock()

    Child()

    assert Parent.__init__.called


def test_init_calls_real_parent_init_2():
    Child()

输出:

$ pytest -q test_src.py -rP
...                                                                                                                                                                                                 [100%]
================================================================================================= PASSES ==================================================================================================
____________________________________________________________________________________ test_init_calls_real_parent_init _____________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Parent __init__ called
Child __init__ called
___________________________________________________________________________________ test_init_calls_updated_parent_init ___________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Child __init__ called
___________________________________________________________________________________ test_init_calls_real_parent_init_2 ____________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Child __init__ called
3 passed in 0.01s

发现:
第一次测试称为真正的 Parent.__init__ .第二次测试称为模拟。然而在第三次测试中，它也意外地调用了第二次测试中的mock。
有修正:

from unittest.mock import Mock, patch

from src import Child, Parent


def test_init_calls_real_parent_init():
    Child()


# Personally I wouldn't advise to do this. It just works :)
def test_init_calls_updated_parent_init():
    # Setup
    orig_parent_init = Parent.__init__  # Store original init

    # Real test
    Parent.__init__ = Mock()

    Child()

    assert Parent.__init__.called

    # Teardown
    Parent.__init__ = orig_parent_init  # Bring back the original init


@patch("src.Parent.__init__")  # Uses unittest
def test_init_calls_mocked_parent_init(mock_parent_init):
    Child()

    assert mock_parent_init.called


def test_init_calls_mocked_parent_init_2(mocker):  # Uses pytest-mock
    mock_parent_init = mocker.patch("src.Parent.__init__")

    Child()

    assert mock_parent_init.called


def test_init_calls_real_parent_init_2():
    Child()

输出:

$ pytest -q test_src_2.py -rP
.....                                                                                                                                                                                               [100%]
================================================================================================= PASSES ==================================================================================================
____________________________________________________________________________________ test_init_calls_real_parent_init _____________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Parent __init__ called
Child __init__ called
___________________________________________________________________________________ test_init_calls_updated_parent_init ___________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Child __init__ called
___________________________________________________________________________________ test_init_calls_mocked_parent_init ____________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Child __init__ called
__________________________________________________________________________________ test_init_calls_mocked_parent_init_2 ___________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Child __init__ called
___________________________________________________________________________________ test_init_calls_real_parent_init_2 ____________________________________________________________________________________
------------------------------------------------------------------------------------------ Captured stdout call -------------------------------------------------------------------------------------------
Parent __init__ called
Child __init__ called
5 passed in 0.03s

发现:
在这里，我使用了 2 个解决方案:

要么改回 Parent.__init__ 的原始实现手动重新分配到模拟后(参见 test_init_calls_updated_parent_init )(不建议)

或者使用 unittest 和 pytest-mock 的内置修补功能(参见 test_init_calls_mocked_parent_init 和 test_init_calls_mocked_parent_init_2 )

现在，第一个和最后一个测试都正确调用了实际的 Parent.__init__ ，即使在所有的 mock 之后。