New submission from Frank Harrison <fr...@doublethefish.com>:
This is my first bug logged here, I've tried to follow the guideline and search
for this issue; please let me know if I missed anything.
Summary:
unittest.mock.MagicMock has a regression starting in 3.8. The regression was
only tested on latest non-prerelease versions of python 3.5, 3.6, 3.7, 3.8 and
3.9. Tested on OSX and Fedora 31.
Repro:
------
If you create an instance of a MagicMock specialisation with parameters to
__init__(), you can no longer pass that instance to the __init__() function of
another MagicMock object e.g. a base-class is replaced with MagicMock. See the
unittests bellow for more details, use-cases and fail situations.
What happens:
-------------
Here's a python3.9 example traceback. It may be worth noting that there is a
difference in the tracebacks between 3.8 and 3.9.
Traceback (most recent call last):
File "<...>", line <..>, in test_raw_magic_moc_passing_thru_single_pos
mock_object = mock.MagicMock(mock_param) # error is here, instantiating
another object
File "/usr/lib64/python3.9/unittest/mock.py", line 408, in __new__
if spec_arg and _is_async_obj(spec_arg):
File "/usr/lib64/python3.9/unittest/mock.py", line 2119, in __get__
return self.create_mock()
File "/usr/lib64/python3.9/unittest/mock.py", line 2112, in create_mock
m = parent._get_child_mock(name=entry, _new_name=entry,
File "/usr/lib64/python3.9/unittest/mock.py", line 1014, in _get_child_mock
return klass(**kw)
TypeError: __init__() got an unexpected keyword argument 'name'
Code demonstrating the problem:
-------------------------------
import unittest
from unittest import mock
class TestMockMagicAssociativeHierarchies(unittest.TestCase):
""" Mimicing real-world testing where we mock a base-class
The intent here is to demonstrate some of the requirements of associative-
hierarchies e.g. where a class may have its associative-parent set at
run-time, rather that defining it via a class-hierarchy. Obviously this
also needs to work with class-hierarchies, that is an associative-parent is
likely to be a specialisation of some interface, usually one that is being
mocked.
For example tkinter and Qt have both a class-hierarchy and a layout-
hierarchy; the latter is modifyable at runtime.
Most of the tests here mimic a specialisation of an upstream object (say a
tk.Frame class), instantiating that specialisation and then passing it to
another object. The reason behind this is an observed regression in Python
3.8.
"""
def test_raw_magic_moc_passing_thru_no_params(self):
""" REGRESSION: Python3.8 (inc Python3.9)
Create a mocked specialisation passing it to another mock.
One real-world use-case for this is simple cases where we simply want to
define a new convenience type that forces a default configuration of
the inherited type (calls super().__init__()).
"""
class MockSubCallsParentInit(mock.MagicMock):
def __init__(self):
super().__init__() # intentionally empty
mock_param = MockSubCallsParentInit()
mock_object = mock.MagicMock(mock_param) # error is here,
instantiating another object
self.assertIsInstance(mock_object, mock.MagicMock)
def test_raw_magic_moc_passing_thru_single_pos(self):
""" REGRESSION: Python3.8 (inc Python3.9)
Same as test_raw_magic_moc_no_init_params() but we want to specialise
with positional arguments. """
class MockSubCallsParentInitWithPositionalParam(mock.MagicMock):
def __init__(self):
super().__init__("specialise init calls")
mock_param = MockSubCallsParentInitWithPositionalParam()
mock_object = mock.MagicMock(mock_param) # error is here,
instantiating another object
self.assertIsInstance(mock_object, mock.MagicMock)
def test_raw_magic_moc_passing_thru_single_kwarg(self):
""" REGRESSION: Python3.8 (inc Python3.9)
Same as test_raw_magic_moc_passing_thru_single_pos() but we want to
specialise with a key-word argument. """
class MockSubCallsParentInitWithPositionalParam(mock.MagicMock):
def __init__(self):
super().__init__(__some_key_word__="some data")
mock_param = MockSubCallsParentInitWithPositionalParam()
mock_object = mock.MagicMock(mock_param) # error is here,
instantiating another object
self.assertIsInstance(mock_object, mock.MagicMock)
def test_mock_as_param_no_inheritance(self):
""" PASSES
Mimic mocking out types, without type specialisation.
for example in pseudo code
tk.Frame = mock.MagicMock; tk.Frame(t.Frame) """
mock_param = mock.MagicMock()
mock_object = mock.MagicMock(mock_param)
self.assertIsInstance(mock_object, mock.MagicMock)
def test_mock_as_param_no_init_override(self):
""" PASSES
Leaves the __init__() function behaviour as default; should always
work. Note that we do not specialise member functions.
Although the intent here is similar to the one captured by
test_raw_magic_moc_passing_thru_no_params(), this is a less likely
usecase, although it does happen, but is here for completeness """
class MockSub(mock.MagicMock): pass
mock_param = MockSub()
mock_object = mock.MagicMock(mock_param)
self.assertIsInstance(mock_object, mock.MagicMock)
def test_init_with_args_n_kwargs_passthru(self):
""" PASSES
Intended to be the same as test_mock_as_param_no_init_override as well
as a base-test for ithe usecases where a user will define more complex
behaviours such as key-word modification, member-variable definitions
and so on. """
class MockSubInitPassThruArgsNKwargs(mock.MagicMock):
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs) # intentionally redundant
mock_param = MockSubInitPassThruArgsNKwargs()
mock_object = mock.MagicMock(mock_param)
self.assertIsInstance(mock_object, mock.MagicMock)
def test_init_with_args_n_kwargs_modify_kwargs(self):
""" PASSES
Same as test_init_with_args_n_kwargs_passthru() but modifies the kwargs
dict on the way through the __init__() function.
"""
class MockSubModifyKwargs(mock.MagicMock):
def __init__(self, *args, **kwargs):
kwargs["__kw args added__"] = "test value"
super().__init__(*args, **kwargs)
mock_param = MockSubModifyKwargs()
mock_object = mock.MagicMock(mock_param)
self.assertIsInstance(mock_object, mock.MagicMock)
def test_init_with_args_n_kwargs_modify_args(self):
""" PASSES
Same as test_init_with_args_n_kwargs_passthru() but modifies the args
on their way through the __init__() function.
"""
class MockSubModifyArgs(mock.MagicMock):
def __init__(self, *args, **kwargs):
super().__init__("test value", *args, **kwargs)
mock_param = MockSubModifyArgs()
mock_object = mock.MagicMock(mock_param)
self.assertIsInstance(mock_object, mock.MagicMock)
----------
components: Library (Lib)
messages: 361552
nosy: Frank Harrison
priority: normal
severity: normal
status: open
title: MagicMock specialisation instance can no longer be passed to new
MagicMock instance
versions: Python 3.8, Python 3.9
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue39578>
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