@example decorator not working with patched test

[fulaphex]

Using @given, @example and @mock.patch on a test that is a method of a TestCase class fails with:

TypeError: test_bar() missing 1 required positional argument: 'self'

Code triggering the exception:

from hypothesis import given, example, strategies
from unittest import mock, TestCase

def bar():
    return 1


class FooTest(TestCase):
    @given(baz=strategies.integers())
    @example(baz=3)
    @mock.patch("foo.bar", lambda: 2)
    def test_bar(self, baz):
        pass
        

Full error:

============================= test session starts ==============================
platform darwin -- Python 3.7.4, pytest-5.2.4, py-1.8.0, pluggy-0.13.0
rootdir: /tmp
plugins: hypothesis-4.47.0
collected 1 item

foo.py F                                                                 [100%]

=================================== FAILURES ===================================
_______________________________ FooTest.test_bar _______________________________

args = (<foo.FooTest testMethod=test_bar>,), keywargs = {}

    @wraps(func)
>   def patched(*args, **keywargs):

/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/mock.py:1194: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/usr/local/lib/python3.7/site-packages/hypothesis/core.py:369: in execute_explicit_examples
    print_example=True,
/usr/local/lib/python3.7/site-packages/hypothesis/core.py:573: in execute_once
    result = self.test_runner(data, run)
/usr/local/lib/python3.7/site-packages/hypothesis/executors.py:56: in default_new_style_executor
    return function(data)
/usr/local/lib/python3.7/site-packages/hypothesis/core.py:569: in run
    return test(*args, **kwargs)
/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/mock.py:1194: in test_bar
    def patched(*args, **keywargs):
/usr/local/lib/python3.7/site-packages/hypothesis/core.py:533: in test
    result = self.test(*args, **kwargs)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

args = (), keywargs = {'baz': 3}, extra_args = []
entered_patchers = [<unittest.mock._patch object at 0x10dcad090>]
exc_info = (<class 'TypeError'>, TypeError("test_bar() missing 1 required positional argument: 'self'"), <traceback object at 0x10dd1a280>)
patching = <unittest.mock._patch object at 0x10dcad090>
arg = <function FooTest.<lambda> at 0x10dc9be60>

    @wraps(func)
    def patched(*args, **keywargs):
        extra_args = []
        entered_patchers = []
    
        exc_info = tuple()
        try:
            for patching in patched.patchings:
                arg = patching.__enter__()
                entered_patchers.append(patching)
                if patching.attribute_name is not None:
                    keywargs.update(arg)
                elif patching.new is DEFAULT:
                    extra_args.append(arg)
    
            args += tuple(extra_args)
>           return func(*args, **keywargs)
E           TypeError: test_bar() missing 1 required positional argument: 'self'

/usr/local/Cellar/python/3.7.4_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/unittest/mock.py:1209: TypeError
---------------------------------- Hypothesis ----------------------------------
Falsifying example: test_bar(baz=3)
============================== 1 failed in 0.16s ===============================

Changing the order of the decorators, putting the @mock.patch as the outermost seems to solve the issue.
I have checked multiple versions of hypothesis, the newest version for which the code above works fine is 4.46.2, it's broken in 4.47.*.

[Zac-HD]

Huh, sounds kinda like #961 but new as of #2216.

The fix will probably involve some awful argspec juggling, and possibly a special case to handle such decorators 😕

[Zac-HD]

Following #3088 and #3095, I'm confident that - unfortunately! - we can't fix this on in Hypothesis; it's a more generic interaction between the behaviour of definition-time nested decorators and the self argument in bound methods.