, we get a warning when a signal arrives
        msg = ('Exception ignored when trying to {action} '
               'to the signal wakeup fd')
        signal.set_wakeup_fd(write.fileno())

        with captured_stderr() as err:
            signal.raise_signal(signum)

        err = err.getvalue()
        if msg not in err:
            raise AssertionError("first set_wakeup_fd() test failed, "
                                 "stderr: %r" % err)

        # And also if warn_on_full_buffer=True
        signal.set_wakeup_fd(write.fileno(), warn_on_full_buffer=True)

        with captured_stderr() as err:
            signal.raise_signal(signum)

        err = err.getvalue()
        if msg not in err:
            raise AssertionError("set_wakeup_fd(warn_on_full_buffer=True) "
                                 "test failed, stderr: %r" % err)

        # But not if warn_on_full_buffer=False
        signal.set_wakeup_fd(write.fileno(), warn_on_full_buffer=False)

        with captured_stderr() as err:
            signal.raise_signal(signum)

        err = err.getvalue()
        if err != "":
            raise AssertionError("set_wakeup_fd(warn_on_full_buffer=False) "
                                 "test failed, stderr: %r" % err)

        # And then check the default again, to make sure warn_on_full_buffer
        # settings don't leak across calls.
        signal.set_wakeup_fd(write.fileno())

        with captured_stderr() as err:
            signal.raise_signal(signum)

        err = err.getvalue()
        if msg not in err:
            raise AssertionError("second set_wakeup_fd() test failed, "
                                 "stderr: %r" % err)

        r