如何修补 `pathlib.Path.exists()` 方法？

Question

我想为单元测试修补 pathlib.Path 对象的 exists() 方法，但我无法让它工作。

我想做的是：

from unittest.mock import patch
from pathlib import Path

def test_move_basic():
    p = Path('~/test.py')
    with patch.object(p, 'exists') as mock_exists:
        mock_exists.return_value = True

但它失败了：

AttributeError: 'PosixPath' object attribute 'exists' is read-only.

有什么想法吗？

Answer 1

您需要修补 class，而不是实例。在 Path class 上修补方法就足够了，因为它为整个 pathlib 库定义了 exists 方法（PosixPath，WindowsPath, PurePosixPath 和 PureWindowsPath 都继承了实现):

>>> from unittest.mock import patch
>>> from pathlib import Path
>>> p = Path('~/test.py')
>>> with patch.object(Path, 'exists') as mock_exists:
...     mock_exists.return_value = True
...     p.exists()
...
True
>>> with patch.object(Path, 'exists') as mock_exists:
...     mock_exists.return_value = False
...     p.exists()
...
False
>>> with patch.object(Path, 'exists') as mock_exists:
...     mock_exists.return_value = 'Anything you like, actually'
...     p.exists()
...
'Anything you like, actually'

pathlib classes 使用 __slots__ 来保持低内存占用，side-effect 它们的实例不支持任意属性分配。

如何修补 `pathlib.Path.exists()` 方法？

How do I patch the `pathlib.Path.exists()` method?

python

unit-testing

mocking

pathlib