New submission from Ben Reilly <brei...@box.com>:
mock.create_autospec is meant to create a mock that will ensure, among other
things, that method calls on the mock correspond to real methods on the
original object and that the arguments match the signature of the original
method. However, if the original method is decorated with a method that returns
a callable object, the signature check may fail.
Attached is a script that demonstrates the error.
The essential part of the script looks like this:
====
def decorator(m):
return Wrapper(m)
class Wrapper(object):
def __init__(self, method):
self.method = method
update_wrapper(self, method)
def __call__(self, instance, *args, **kwargs):
return self.__get__(instance, type(instance))(*args, **kwargs)
def __get__(self, instance, owner):
... # do the wrapping
====
The `decorator` method returns an instance of the `Wrapper` class, which is
callable. Mock will calculate the signature of a method wrapped with
`decorator` to be equal to that of `Wrapper.__call__`, namely `(instance,
*args, **kwargs)`. Consequently, calls to the mocked method...
1. will incorrectly fail if the method usually takes no arguments, and
2. will incorrectly pass if the method takes at least one argument but too many
arguments are provided.
This list of incorrect behaviour is not exhaustive, but hopefully you get the
point.
If anyone's concerned about real-life examples, this kind of wrapper is used,
for example, in the public Box SDK, as shown here:
https://github.com/box/box-python-sdk/blob/b7f41d9a3f8be0ff3622a0c417bf31d2fbbee969/boxsdk/util/api_call_decorator.py#L10
----------
files: decorator.py
messages: 356159
nosy: breilly_box
priority: normal
severity: normal
status: open
title: mock.create_autospec generates incorrect signature for some decorated
methods
type: behavior
versions: Python 3.7
Added file: https://bugs.python.org/file48698/decorator.py
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue38729>
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