Signal connected to unittest.Mock and MagicMock does not work in Python 3.8

[Homeopatch]

After upgrading Blinker from 1.5 to 1.6.2, tests in my project started to fail.

In short, I found this issue and also suggesting a workaround. Whole test case for reproducing this issue is here.

---

My test cases are checking if a signal was called. I use MagicMock to check if and how signals are called. I also used spec parameter of MagicMock, because plain initialization did not work for some other compatibility issues, you'll see it below

Here is an equivalent of what I have in my tests:

def foo(sender, **kwargs):
    """Stub function for spec parameter"""
    pass

# Test case code
mock = MagicMock(spec=foo)
self.signal.connect(mock, sender=self)
self.signal.send(self) # RuntimeError: Cannot send to a coroutine function here
# see this for details: https://bugs.python.org/issue37251
mock.assert_called_once_with(self)

Stack trace

Error
Traceback (most recent call last):
  File "/home/denis/devel/python_scripts/test_blinker.py", line 24, in test_magicmock_spec
    self.signal.send(self)  # RuntimeError: Cannot send to a coroutine function here
  File "/home/denis/devel/uvis/venv3/lib/python3.8/site-packages/blinker/base.py", line 298, in send
    raise RuntimeError("Cannot send to a coroutine function")
RuntimeError: Cannot send to a coroutine function

So Blinker received async support after the upgrade. The check
asyncio.iscoroutinefunction(func) has been added to send(), where func is my MagicMock. This is indeed a problem
of Python, rather than Blinker, I found this ticket here: https://bugs.python.org/issue37251

So I've tried to get rid of spec

But receive another error, at connect()

def test_magicmock(self):
    mock = MagicMock()
    self.signal.connect(mock, sender=self)  # AttributeError: __self__
    self.signal.send(self)
    mock.assert_called_once_with(self)

Stack trace

Error
Traceback (most recent call last):
  File "/home/denis/devel/python_scripts/test_blinker.py", line 30, in test_magicmock
    self.signal.connect(mock, sender=self)  # AttributeError: __self__
  File "/home/denis/devel/uvis/venv3/lib/python3.8/site-packages/blinker/base.py", line 131, in connect
    receiver_ref = reference(receiver, self._cleanup_receiver)
  File "/home/denis/devel/uvis/venv3/lib/python3.8/site-packages/blinker/_utilities.py", line 80, in reference
    weak = callable_reference(object, callback)
  File "/home/denis/devel/uvis/venv3/lib/python3.8/site-packages/blinker/_utilities.py", line 91, in callable_reference
    return BoundMethodWeakref(target=object, on_delete=callback)
  File "/home/denis/devel/uvis/venv3/lib/python3.8/site-packages/blinker/_saferef.py", line 124, in __new__
    key = cls.calculate_key(target)
  File "/home/denis/devel/uvis/venv3/lib/python3.8/site-packages/blinker/_saferef.py", line 190, in calculate_key
    return (id(get_self(target)), id(get_func(target)))
  File "/usr/lib/python3.8/unittest/mock.py", line 639, in __getattr__
    raise AttributeError(name)
AttributeError: __self__

Plain MagicMock does not work. The same for Mock.

Workaround

Have a callable class and pass it to spec parameter:

class FooStub:
    """Stub class for spec"""
    def __call__(self, sender, **kwargs):
        pass

    ...
def test_magicmock_stub(self):
    # This test passes
    mock = MagicMock(spec=FooStub)
    self.signal.connect(mock, sender=self)
    self.signal.send(self)
    mock.assert_called_once_with(self)

Also works for Mock.

See the code here

[davidism]

Closing as this seems like something Python needs to fix.