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[3.6] bpo-29403: Fix mock's broken autospec behavior on method-bound …

…builtin functions (GH-3)

Cython will, in the right circumstances, offer a MethodType instance
where im_func is a builtin function. Any instance of MethodType is
automatically assumed to be a Python-defined function (more
specifically, a function that has an inspectable signature), but
_set_signature was still conservative in its assumptions. As a result
_set_signature would return early with None instead of a mock since
the im_func had no inspectable signature. This causes problems
deeper inside mock, as _set_signature is assumed to _always_
return a mock, and nothing checked its return value.

In similar corner cases, autospec will simply not check the spec of the
function, so _set_signature is amended to now return early with the
original, not-wrapped mock object.

Patch by Aaron Gallagher.

(cherry picked from commit 856cbcc)
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berkerpeksag committed Jul 21, 2017
1 parent bb323b2 commit 64b9a15886840df422c5203fad25c9801b4cf61e
@@ -165,7 +165,7 @@ def _set_signature(mock, original, instance=False):
skipfirst = isinstance(original, type)
result = _get_signature_object(original, instance, skipfirst)
if result is None:
return mock
func, sig = result
def checksig(*args, **kwargs):
sig.bind(*args, **kwargs)
@@ -1,3 +1,5 @@
import time
import types
import unittest

from unittest.mock import (
@@ -856,6 +858,19 @@ def check_data_descriptor(mock_attr):

def test_autospec_on_bound_builtin_function(self):
meth = types.MethodType(time.ctime, time.time())
self.assertIsInstance(meth(), str)
mocked = create_autospec(meth)

# no signature, so no spec to check against
mocked(4, 5, 6)
mocked.assert_called_once_with(4, 5, 6)

class TestCallList(unittest.TestCase):

def test_args_list_contains_call_list(self):
@@ -0,0 +1,2 @@
Fix ``unittest.mock``'s autospec to not fail on method-bound builtin
functions. Patch by Aaron Gallagher.

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