def test_childSignalHandling(self):
        """
        The disposition of signals which are ignored in the parent
        process is reset to the default behavior for the child
        process.
        """
        # Somewhat arbitrarily select SIGUSR1 here.  It satisfies our
        # requirements that:
        #    - The interpreter not fiddle around with the handler
        #      behind our backs at startup time (this disqualifies
        #      signals like SIGINT and SIGPIPE).
        #    - The default behavior is to exit.
        #
        # This lets us send the signal to the child and then verify
        # that it exits with a status code indicating that it was
        # indeed the signal which caused it to exit.
        which = signal.SIGUSR1

        # Ignore the signal in the parent (and make sure we clean it
        # up).
        handler = signal.signal(which, signal.SIG_IGN)
        self.addCleanup(signal.signal, signal.SIGUSR1, handler)

        # Now do the test.
        return self._testSignal(signal.SIGUSR1)

        The disposition of signals which are ignored in the parent
        process is reset to the default behavior for the child
        process.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_process.py