Blinker Signal connected to unittest.Mock and MagicMock does not work in Python 3.8 test case and workaround

blinker_mock.py

import unittest
from unittest.mock import MagicMock, Mock

from blinker import Signal


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


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


class TestMocks(unittest.TestCase):
    def setUp(self) -> None:
        self.signal = Signal()

    def test_magicmock_spec(self):
        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)

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

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

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

    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)