def test_connectToUncleanServer(self):
        """
        If passed C{True} for the C{checkPID} parameter, a client connection
        attempt made with L{IReactorUNIX.connectUNIX} fails with
        L{error.BadFileError}.
        """
        def ranStupidChild(ign):
            d = defer.Deferred()
            f = FailedConnectionClientFactory(d)
            reactor.connectUNIX(self.filename, f, checkPID=True)
            return self.assertFailure(d, error.BadFileError)
        return self._uncleanSocketTest(ranStupidChild)

        If passed C{True} for the C{checkPID} parameter, a client connection
        attempt made with L{IReactorUNIX.connectUNIX} fails with
        L{error.BadFileError}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_unix.py