不能用pytest-mock模拟'os.path.join‘

Question

当我使用mock库时，例如with mock.patch('os.path.join'):，一切正常，但是当我像这样使用pytest-mock时，如果断言失败，我会得到以下错误：

pytest似乎试图使用'os.path‘模块，但由于它是用mocker打补丁的，它失败了，并引发了错误，我做错了什么吗？

AssertionError: Expected 'transform_file' to be called once. Called 0 times.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 890, in _find_spec
AttributeError: 'AssertionRewritingHook' object has no attribute 'find_spec'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\anaconda\lib\site-packages\py\_path\common.py", line 29, in fspath
    return path_type.__fspath__(path)
AttributeError: type object 'MagicMock' has no attribute '__fspath__'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "c:\anaconda\lib\site-packages\py\_path\local.py", line 152, in __init__
    path = fspath(path)
  File "c:\anaconda\lib\site-packages\py\_path\common.py", line 42, in fspath
    + path_type.__name__)
TypeError: expected str, bytes or os.PathLike object, not MagicMock
... etc etc

Answer 1

要模拟或者更确切地说单元测试os.path.join，您可以使用monkeypatch，因为您已经在使用py.test，例如source

# content of test_module.py
import os.path
def getssh(): # pseudo application code
    return os.path.join(os.path.expanduser("~admin"), '.ssh')

def test_mytest(monkeypatch):
    def mockreturn(path):
        return '/abc'
    monkeypatch.setattr(os.path, 'expanduser', mockreturn)
    x = getssh()
    assert x == '/abc/.ssh'