cpython/Lib/test/test_asyncio/test_unix_events.py

"""Tests for unix_events.py."""

import collections
import gc
import errno
import io
import os
import pprint
import signal
import stat
import sys
import threading
import unittest
import unittest.mock

if sys.platform == 'win32':
    raise unittest.SkipTest('UNIX only')


import asyncio
from asyncio import log
from asyncio import test_utils
from asyncio import unix_events


@unittest.skipUnless(signal, 'Signals are not supported')
class SelectorEventLoopTests(unittest.TestCase):

    def setUp(self):
        self.loop = asyncio.SelectorEventLoop()
        asyncio.set_event_loop(None)

    def tearDown(self):
        self.loop.close()

    def test_check_signal(self):
        self.assertRaises(
            TypeError, self.loop._check_signal, '1')
        self.assertRaises(
            ValueError, self.loop._check_signal, signal.NSIG + 1)

    def test_handle_signal_no_handler(self):
        self.loop._handle_signal(signal.NSIG + 1, ())

    def test_handle_signal_cancelled_handler(self):
        h = asyncio.Handle(unittest.mock.Mock(), ())
        h.cancel()
        self.loop._signal_handlers[signal.NSIG + 1] = h
        self.loop.remove_signal_handler = unittest.mock.Mock()
        self.loop._handle_signal(signal.NSIG + 1, ())
        self.loop.remove_signal_handler.assert_called_with(signal.NSIG + 1)

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_add_signal_handler_setup_error(self, m_signal):
        m_signal.NSIG = signal.NSIG
        m_signal.set_wakeup_fd.side_effect = ValueError

        self.assertRaises(
            RuntimeError,
            self.loop.add_signal_handler,
            signal.SIGINT, lambda: True)

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_add_signal_handler(self, m_signal):
        m_signal.NSIG = signal.NSIG

        cb = lambda: True
        self.loop.add_signal_handler(signal.SIGHUP, cb)
        h = self.loop._signal_handlers.get(signal.SIGHUP)
        self.assertIsInstance(h, asyncio.Handle)
        self.assertEqual(h._callback, cb)

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_add_signal_handler_install_error(self, m_signal):
        m_signal.NSIG = signal.NSIG

        def set_wakeup_fd(fd):
            if fd == -1:
                raise ValueError()
        m_signal.set_wakeup_fd = set_wakeup_fd

        class Err(OSError):
            errno = errno.EFAULT
        m_signal.signal.side_effect = Err

        self.assertRaises(
            Err,
            self.loop.add_signal_handler,
            signal.SIGINT, lambda: True)

    @unittest.mock.patch('asyncio.unix_events.signal')
    @unittest.mock.patch('asyncio.unix_events.logger')
    def test_add_signal_handler_install_error2(self, m_logging, m_signal):
        m_signal.NSIG = signal.NSIG

        class Err(OSError):
            errno = errno.EINVAL
        m_signal.signal.side_effect = Err

        self.loop._signal_handlers[signal.SIGHUP] = lambda: True
        self.assertRaises(
            RuntimeError,
            self.loop.add_signal_handler,
            signal.SIGINT, lambda: True)
        self.assertFalse(m_logging.info.called)
        self.assertEqual(1, m_signal.set_wakeup_fd.call_count)

    @unittest.mock.patch('asyncio.unix_events.signal')
    @unittest.mock.patch('asyncio.unix_events.logger')
    def test_add_signal_handler_install_error3(self, m_logging, m_signal):
        class Err(OSError):
            errno = errno.EINVAL
        m_signal.signal.side_effect = Err
        m_signal.NSIG = signal.NSIG

        self.assertRaises(
            RuntimeError,
            self.loop.add_signal_handler,
            signal.SIGINT, lambda: True)
        self.assertFalse(m_logging.info.called)
        self.assertEqual(2, m_signal.set_wakeup_fd.call_count)

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_remove_signal_handler(self, m_signal):
        m_signal.NSIG = signal.NSIG

        self.loop.add_signal_handler(signal.SIGHUP, lambda: True)

        self.assertTrue(
            self.loop.remove_signal_handler(signal.SIGHUP))
        self.assertTrue(m_signal.set_wakeup_fd.called)
        self.assertTrue(m_signal.signal.called)
        self.assertEqual(
            (signal.SIGHUP, m_signal.SIG_DFL), m_signal.signal.call_args[0])

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_remove_signal_handler_2(self, m_signal):
        m_signal.NSIG = signal.NSIG
        m_signal.SIGINT = signal.SIGINT

        self.loop.add_signal_handler(signal.SIGINT, lambda: True)
        self.loop._signal_handlers[signal.SIGHUP] = object()
        m_signal.set_wakeup_fd.reset_mock()

        self.assertTrue(
            self.loop.remove_signal_handler(signal.SIGINT))
        self.assertFalse(m_signal.set_wakeup_fd.called)
        self.assertTrue(m_signal.signal.called)
        self.assertEqual(
            (signal.SIGINT, m_signal.default_int_handler),
            m_signal.signal.call_args[0])

    @unittest.mock.patch('asyncio.unix_events.signal')
    @unittest.mock.patch('asyncio.unix_events.logger')
    def test_remove_signal_handler_cleanup_error(self, m_logging, m_signal):
        m_signal.NSIG = signal.NSIG
        self.loop.add_signal_handler(signal.SIGHUP, lambda: True)

        m_signal.set_wakeup_fd.side_effect = ValueError

        self.loop.remove_signal_handler(signal.SIGHUP)
        self.assertTrue(m_logging.info)

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_remove_signal_handler_error(self, m_signal):
        m_signal.NSIG = signal.NSIG
        self.loop.add_signal_handler(signal.SIGHUP, lambda: True)

        m_signal.signal.side_effect = OSError

        self.assertRaises(
            OSError, self.loop.remove_signal_handler, signal.SIGHUP)

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_remove_signal_handler_error2(self, m_signal):
        m_signal.NSIG = signal.NSIG
        self.loop.add_signal_handler(signal.SIGHUP, lambda: True)

        class Err(OSError):
            errno = errno.EINVAL
        m_signal.signal.side_effect = Err

        self.assertRaises(
            RuntimeError, self.loop.remove_signal_handler, signal.SIGHUP)

    @unittest.mock.patch('asyncio.unix_events.signal')
    def test_close(self, m_signal):
        m_signal.NSIG = signal.NSIG

        self.loop.add_signal_handler(signal.SIGHUP, lambda: True)
        self.loop.add_signal_handler(signal.SIGCHLD, lambda: True)

        self.assertEqual(len(self.loop._signal_handlers), 2)

        m_signal.set_wakeup_fd.reset_mock()

        self.loop.close()

        self.assertEqual(len(self.loop._signal_handlers), 0)
        m_signal.set_wakeup_fd.assert_called_once_with(-1)


class UnixReadPipeTransportTests(unittest.TestCase):

    def setUp(self):
        self.loop = test_utils.TestLoop()
        self.protocol = test_utils.make_test_protocol(asyncio.Protocol)
        self.pipe = unittest.mock.Mock(spec_set=io.RawIOBase)
        self.pipe.fileno.return_value = 5

        fcntl_patcher = unittest.mock.patch('fcntl.fcntl')
        fcntl_patcher.start()
        self.addCleanup(fcntl_patcher.stop)

        fstat_patcher = unittest.mock.patch('os.fstat')
        m_fstat = fstat_patcher.start()
        st = unittest.mock.Mock()
        st.st_mode = stat.S_IFIFO
        m_fstat.return_value = st
        self.addCleanup(fstat_patcher.stop)

    def test_ctor(self):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)
        self.loop.assert_reader(5, tr._read_ready)
        test_utils.run_briefly(self.loop)
        self.protocol.connection_made.assert_called_with(tr)

    def test_ctor_with_waiter(self):
        fut = asyncio.Future(loop=self.loop)
        unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol, fut)
        test_utils.run_briefly(self.loop)
        self.assertIsNone(fut.result())

    @unittest.mock.patch('os.read')
    def test__read_ready(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)
        m_read.return_value = b'data'
        tr._read_ready()

        m_read.assert_called_with(5, tr.max_size)
        self.protocol.data_received.assert_called_with(b'data')

    @unittest.mock.patch('os.read')
    def test__read_ready_eof(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)
        m_read.return_value = b''
        tr._read_ready()

        m_read.assert_called_with(5, tr.max_size)
        self.assertFalse(self.loop.readers)
        test_utils.run_briefly(self.loop)
        self.protocol.eof_received.assert_called_with()
        self.protocol.connection_lost.assert_called_with(None)

    @unittest.mock.patch('os.read')
    def test__read_ready_blocked(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)
        m_read.side_effect = BlockingIOError
        tr._read_ready()

        m_read.assert_called_with(5, tr.max_size)
        test_utils.run_briefly(self.loop)
        self.assertFalse(self.protocol.data_received.called)

    @unittest.mock.patch('asyncio.log.logger.exception')
    @unittest.mock.patch('os.read')
    def test__read_ready_error(self, m_read, m_logexc):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)
        err = OSError()
        m_read.side_effect = err
        tr._close = unittest.mock.Mock()
        tr._read_ready()

        m_read.assert_called_with(5, tr.max_size)
        tr._close.assert_called_with(err)
        m_logexc.assert_called_with('Fatal error for %s', tr)

    @unittest.mock.patch('os.read')
    def test_pause_reading(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)

        m = unittest.mock.Mock()
        self.loop.add_reader(5, m)
        tr.pause_reading()
        self.assertFalse(self.loop.readers)

    @unittest.mock.patch('os.read')
    def test_resume_reading(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)

        tr.resume_reading()
        self.loop.assert_reader(5, tr._read_ready)

    @unittest.mock.patch('os.read')
    def test_close(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)

        tr._close = unittest.mock.Mock()
        tr.close()
        tr._close.assert_called_with(None)

    @unittest.mock.patch('os.read')
    def test_close_already_closing(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)

        tr._closing = True
        tr._close = unittest.mock.Mock()
        tr.close()
        self.assertFalse(tr._close.called)

    @unittest.mock.patch('os.read')
    def test__close(self, m_read):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)

        err = object()
        tr._close(err)
        self.assertTrue(tr._closing)
        self.assertFalse(self.loop.readers)
        test_utils.run_briefly(self.loop)
        self.protocol.connection_lost.assert_called_with(err)

    def test__call_connection_lost(self):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)

        err = None
        tr._call_connection_lost(err)
        self.protocol.connection_lost.assert_called_with(err)
        self.pipe.close.assert_called_with()

        self.assertIsNone(tr._protocol)
        self.assertEqual(2, sys.getrefcount(self.protocol),
                         pprint.pformat(gc.get_referrers(self.protocol)))
        self.assertIsNone(tr._loop)
        self.assertEqual(2, sys.getrefcount(self.loop),
                         pprint.pformat(gc.get_referrers(self.loop)))

    def test__call_connection_lost_with_err(self):
        tr = unix_events._UnixReadPipeTransport(
            self.loop, self.pipe, self.protocol)

        err = OSError()
        tr._call_connection_lost(err)
        self.protocol.connection_lost.assert_called_with(err)
        self.pipe.close.assert_called_with()

        self.assertIsNone(tr._protocol)
        self.assertEqual(2, sys.getrefcount(self.protocol),
                         pprint.pformat(gc.get_referrers(self.protocol)))
        self.assertIsNone(tr._loop)
        self.assertEqual(2, sys.getrefcount(self.loop),
                         pprint.pformat(gc.get_referrers(self.loop)))


class UnixWritePipeTransportTests(unittest.TestCase):

    def setUp(self):
        self.loop = test_utils.TestLoop()
        self.protocol = test_utils.make_test_protocol(asyncio.BaseProtocol)
        self.pipe = unittest.mock.Mock(spec_set=io.RawIOBase)
        self.pipe.fileno.return_value = 5

        fcntl_patcher = unittest.mock.patch('fcntl.fcntl')
        fcntl_patcher.start()
        self.addCleanup(fcntl_patcher.stop)

        fstat_patcher = unittest.mock.patch('os.fstat')
        m_fstat = fstat_patcher.start()
        st = unittest.mock.Mock()
        st.st_mode = stat.S_IFSOCK
        m_fstat.return_value = st
        self.addCleanup(fstat_patcher.stop)

    def test_ctor(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)
        self.loop.assert_reader(5, tr._read_ready)
        test_utils.run_briefly(self.loop)
        self.protocol.connection_made.assert_called_with(tr)

    def test_ctor_with_waiter(self):
        fut = asyncio.Future(loop=self.loop)
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol, fut)
        self.loop.assert_reader(5, tr._read_ready)
        test_utils.run_briefly(self.loop)
        self.assertEqual(None, fut.result())

    def test_can_write_eof(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)
        self.assertTrue(tr.can_write_eof())

    @unittest.mock.patch('os.write')
    def test_write(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        m_write.return_value = 4
        tr.write(b'data')
        m_write.assert_called_with(5, b'data')
        self.assertFalse(self.loop.writers)
        self.assertEqual([], tr._buffer)

    @unittest.mock.patch('os.write')
    def test_write_no_data(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        tr.write(b'')
        self.assertFalse(m_write.called)
        self.assertFalse(self.loop.writers)
        self.assertEqual([], tr._buffer)

    @unittest.mock.patch('os.write')
    def test_write_partial(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        m_write.return_value = 2
        tr.write(b'data')
        m_write.assert_called_with(5, b'data')
        self.loop.assert_writer(5, tr._write_ready)
        self.assertEqual([b'ta'], tr._buffer)

    @unittest.mock.patch('os.write')
    def test_write_buffer(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        self.loop.add_writer(5, tr._write_ready)
        tr._buffer = [b'previous']
        tr.write(b'data')
        self.assertFalse(m_write.called)
        self.loop.assert_writer(5, tr._write_ready)
        self.assertEqual([b'previous', b'data'], tr._buffer)

    @unittest.mock.patch('os.write')
    def test_write_again(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        m_write.side_effect = BlockingIOError()
        tr.write(b'data')
        m_write.assert_called_with(5, b'data')
        self.loop.assert_writer(5, tr._write_ready)
        self.assertEqual([b'data'], tr._buffer)

    @unittest.mock.patch('asyncio.unix_events.logger')
    @unittest.mock.patch('os.write')
    def test_write_err(self, m_write, m_log):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        err = OSError()
        m_write.side_effect = err
        tr._fatal_error = unittest.mock.Mock()
        tr.write(b'data')
        m_write.assert_called_with(5, b'data')
        self.assertFalse(self.loop.writers)
        self.assertEqual([], tr._buffer)
        tr._fatal_error.assert_called_with(err)
        self.assertEqual(1, tr._conn_lost)

        tr.write(b'data')
        self.assertEqual(2, tr._conn_lost)
        tr.write(b'data')
        tr.write(b'data')
        tr.write(b'data')
        tr.write(b'data')
        # This is a bit overspecified. :-(
        m_log.warning.assert_called_with(
            'pipe closed by peer or os.write(pipe, data) raised exception.')

    @unittest.mock.patch('os.write')
    def test_write_close(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)
        tr._read_ready()  # pipe was closed by peer

        tr.write(b'data')
        self.assertEqual(tr._conn_lost, 1)
        tr.write(b'data')
        self.assertEqual(tr._conn_lost, 2)

    def test__read_ready(self):
        tr = unix_events._UnixWritePipeTransport(self.loop, self.pipe,
                                                 self.protocol)
        tr._read_ready()
        self.assertFalse(self.loop.readers)
        self.assertFalse(self.loop.writers)
        self.assertTrue(tr._closing)
        test_utils.run_briefly(self.loop)
        self.protocol.connection_lost.assert_called_with(None)

    @unittest.mock.patch('os.write')
    def test__write_ready(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)
        self.loop.add_writer(5, tr._write_ready)
        tr._buffer = [b'da', b'ta']
        m_write.return_value = 4
        tr._write_ready()
        m_write.assert_called_with(5, b'data')
        self.assertFalse(self.loop.writers)
        self.assertEqual([], tr._buffer)

    @unittest.mock.patch('os.write')
    def test__write_ready_partial(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        self.loop.add_writer(5, tr._write_ready)
        tr._buffer = [b'da', b'ta']
        m_write.return_value = 3
        tr._write_ready()
        m_write.assert_called_with(5, b'data')
        self.loop.assert_writer(5, tr._write_ready)
        self.assertEqual([b'a'], tr._buffer)

    @unittest.mock.patch('os.write')
    def test__write_ready_again(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        self.loop.add_writer(5, tr._write_ready)
        tr._buffer = [b'da', b'ta']
        m_write.side_effect = BlockingIOError()
        tr._write_ready()
        m_write.assert_called_with(5, b'data')
        self.loop.assert_writer(5, tr._write_ready)
        self.assertEqual([b'data'], tr._buffer)

    @unittest.mock.patch('os.write')
    def test__write_ready_empty(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        self.loop.add_writer(5, tr._write_ready)
        tr._buffer = [b'da', b'ta']
        m_write.return_value = 0
        tr._write_ready()
        m_write.assert_called_with(5, b'data')
        self.loop.assert_writer(5, tr._write_ready)
        self.assertEqual([b'data'], tr._buffer)

    @unittest.mock.patch('asyncio.log.logger.exception')
    @unittest.mock.patch('os.write')
    def test__write_ready_err(self, m_write, m_logexc):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        self.loop.add_writer(5, tr._write_ready)
        tr._buffer = [b'da', b'ta']
        m_write.side_effect = err = OSError()
        tr._write_ready()
        m_write.assert_called_with(5, b'data')
        self.assertFalse(self.loop.writers)
        self.assertFalse(self.loop.readers)
        self.assertEqual([], tr._buffer)
        self.assertTrue(tr._closing)
        m_logexc.assert_called_with('Fatal error for %s', tr)
        self.assertEqual(1, tr._conn_lost)
        test_utils.run_briefly(self.loop)
        self.protocol.connection_lost.assert_called_with(err)

    @unittest.mock.patch('os.write')
    def test__write_ready_closing(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        self.loop.add_writer(5, tr._write_ready)
        tr._closing = True
        tr._buffer = [b'da', b'ta']
        m_write.return_value = 4
        tr._write_ready()
        m_write.assert_called_with(5, b'data')
        self.assertFalse(self.loop.writers)
        self.assertFalse(self.loop.readers)
        self.assertEqual([], tr._buffer)
        self.protocol.connection_lost.assert_called_with(None)
        self.pipe.close.assert_called_with()

    @unittest.mock.patch('os.write')
    def test_abort(self, m_write):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        self.loop.add_writer(5, tr._write_ready)
        self.loop.add_reader(5, tr._read_ready)
        tr._buffer = [b'da', b'ta']
        tr.abort()
        self.assertFalse(m_write.called)
        self.assertFalse(self.loop.readers)
        self.assertFalse(self.loop.writers)
        self.assertEqual([], tr._buffer)
        self.assertTrue(tr._closing)
        test_utils.run_briefly(self.loop)
        self.protocol.connection_lost.assert_called_with(None)

    def test__call_connection_lost(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        err = None
        tr._call_connection_lost(err)
        self.protocol.connection_lost.assert_called_with(err)
        self.pipe.close.assert_called_with()

        self.assertIsNone(tr._protocol)
        self.assertEqual(2, sys.getrefcount(self.protocol),
                         pprint.pformat(gc.get_referrers(self.protocol)))
        self.assertIsNone(tr._loop)
        self.assertEqual(2, sys.getrefcount(self.loop),
                         pprint.pformat(gc.get_referrers(self.loop)))

    def test__call_connection_lost_with_err(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        err = OSError()
        tr._call_connection_lost(err)
        self.protocol.connection_lost.assert_called_with(err)
        self.pipe.close.assert_called_with()

        self.assertIsNone(tr._protocol)
        self.assertEqual(2, sys.getrefcount(self.protocol),
                         pprint.pformat(gc.get_referrers(self.protocol)))
        self.assertIsNone(tr._loop)
        self.assertEqual(2, sys.getrefcount(self.loop),
                         pprint.pformat(gc.get_referrers(self.loop)))

    def test_close(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        tr.write_eof = unittest.mock.Mock()
        tr.close()
        tr.write_eof.assert_called_with()

    def test_close_closing(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        tr.write_eof = unittest.mock.Mock()
        tr._closing = True
        tr.close()
        self.assertFalse(tr.write_eof.called)

    def test_write_eof(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)

        tr.write_eof()
        self.assertTrue(tr._closing)
        self.assertFalse(self.loop.readers)
        test_utils.run_briefly(self.loop)
        self.protocol.connection_lost.assert_called_with(None)

    def test_write_eof_pending(self):
        tr = unix_events._UnixWritePipeTransport(
            self.loop, self.pipe, self.protocol)
        tr._buffer = [b'data']
        tr.write_eof()
        self.assertTrue(tr._closing)
        self.assertFalse(self.protocol.connection_lost.called)


class AbstractChildWatcherTests(unittest.TestCase):

    def test_not_implemented(self):
        f = unittest.mock.Mock()
        watcher = asyncio.AbstractChildWatcher()
        self.assertRaises(
            NotImplementedError, watcher.add_child_handler, f, f)
        self.assertRaises(
            NotImplementedError, watcher.remove_child_handler, f)
        self.assertRaises(
            NotImplementedError, watcher.attach_loop, f)
        self.assertRaises(
            NotImplementedError, watcher.close)
        self.assertRaises(
            NotImplementedError, watcher.__enter__)
        self.assertRaises(
            NotImplementedError, watcher.__exit__, f, f, f)


class BaseChildWatcherTests(unittest.TestCase):

    def test_not_implemented(self):
        f = unittest.mock.Mock()
        watcher = unix_events.BaseChildWatcher()
        self.assertRaises(
            NotImplementedError, watcher._do_waitpid, f)


WaitPidMocks = collections.namedtuple("WaitPidMocks",
                                      ("waitpid",
                                       "WIFEXITED",
                                       "WIFSIGNALED",
                                       "WEXITSTATUS",
                                       "WTERMSIG",
                                       ))


class ChildWatcherTestsMixin:

    ignore_warnings = unittest.mock.patch.object(log.logger, "warning")

    def setUp(self):
        self.loop = test_utils.TestLoop()
        self.running = False
        self.zombies = {}

        with unittest.mock.patch.object(
                self.loop, "add_signal_handler") as self.m_add_signal_handler:
            self.watcher = self.create_watcher()
            self.watcher.attach_loop(self.loop)

    def waitpid(self, pid, flags):
        if isinstance(self.watcher, asyncio.SafeChildWatcher) or pid != -1:
            self.assertGreater(pid, 0)
        try:
            if pid < 0:
                return self.zombies.popitem()
            else:
                return pid, self.zombies.pop(pid)
        except KeyError:
            pass
        if self.running:
            return 0, 0
        else:
            raise ChildProcessError()

    def add_zombie(self, pid, returncode):
        self.zombies[pid] = returncode + 32768

    def WIFEXITED(self, status):
        return status >= 32768

    def WIFSIGNALED(self, status):
        return 32700 < status < 32768

    def WEXITSTATUS(self, status):
        self.assertTrue(self.WIFEXITED(status))
        return status - 32768

    def WTERMSIG(self, status):
        self.assertTrue(self.WIFSIGNALED(status))
        return 32768 - status

    def test_create_watcher(self):
        self.m_add_signal_handler.assert_called_once_with(
            signal.SIGCHLD, self.watcher._sig_chld)

    def waitpid_mocks(func):
        def wrapped_func(self):
            def patch(target, wrapper):
                return unittest.mock.patch(target, wraps=wrapper,
                                           new_callable=unittest.mock.Mock)

            with patch('os.WTERMSIG', self.WTERMSIG) as m_WTERMSIG, \
                 patch('os.WEXITSTATUS', self.WEXITSTATUS) as m_WEXITSTATUS, \
                 patch('os.WIFSIGNALED', self.WIFSIGNALED) as m_WIFSIGNALED, \
                 patch('os.WIFEXITED', self.WIFEXITED) as m_WIFEXITED, \
                 patch('os.waitpid', self.waitpid) as m_waitpid:
                func(self, WaitPidMocks(m_waitpid,
                                        m_WIFEXITED, m_WIFSIGNALED,
                                        m_WEXITSTATUS, m_WTERMSIG,
                                        ))
        return wrapped_func

    @waitpid_mocks
    def test_sigchld(self, m):
        # register a child
        callback = unittest.mock.Mock()

        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(42, callback, 9, 10, 14)

        self.assertFalse(callback.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child is running
        self.watcher._sig_chld()

        self.assertFalse(callback.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child terminates (returncode 12)
        self.running = False
        self.add_zombie(42, 12)
        self.watcher._sig_chld()

        self.assertTrue(m.WIFEXITED.called)
        self.assertTrue(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)
        callback.assert_called_once_with(42, 12, 9, 10, 14)

        m.WIFSIGNALED.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WEXITSTATUS.reset_mock()
        callback.reset_mock()

        # ensure that the child is effectively reaped
        self.add_zombie(42, 13)
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback.called)
        self.assertFalse(m.WTERMSIG.called)

        m.WIFSIGNALED.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WEXITSTATUS.reset_mock()

        # sigchld called again
        self.zombies.clear()
        self.watcher._sig_chld()

        self.assertFalse(callback.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

    @waitpid_mocks
    def test_sigchld_two_children(self, m):
        callback1 = unittest.mock.Mock()
        callback2 = unittest.mock.Mock()

        # register child 1
        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(43, callback1, 7, 8)

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # register child 2
        with self.watcher:
            self.watcher.add_child_handler(44, callback2, 147, 18)

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # childen are running
        self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child 1 terminates (signal 3)
        self.add_zombie(43, -3)
        self.watcher._sig_chld()

        callback1.assert_called_once_with(43, -3, 7, 8)
        self.assertFalse(callback2.called)
        self.assertTrue(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertTrue(m.WTERMSIG.called)

        m.WIFSIGNALED.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WTERMSIG.reset_mock()
        callback1.reset_mock()

        # child 2 still running
        self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child 2 terminates (code 108)
        self.add_zombie(44, 108)
        self.running = False
        self.watcher._sig_chld()

        callback2.assert_called_once_with(44, 108, 147, 18)
        self.assertFalse(callback1.called)
        self.assertTrue(m.WIFEXITED.called)
        self.assertTrue(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        m.WIFSIGNALED.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WEXITSTATUS.reset_mock()
        callback2.reset_mock()

        # ensure that the children are effectively reaped
        self.add_zombie(43, 14)
        self.add_zombie(44, 15)
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WTERMSIG.called)

        m.WIFSIGNALED.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WEXITSTATUS.reset_mock()

        # sigchld called again
        self.zombies.clear()
        self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

    @waitpid_mocks
    def test_sigchld_two_children_terminating_together(self, m):
        callback1 = unittest.mock.Mock()
        callback2 = unittest.mock.Mock()

        # register child 1
        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(45, callback1, 17, 8)

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # register child 2
        with self.watcher:
            self.watcher.add_child_handler(46, callback2, 1147, 18)

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # childen are running
        self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child 1 terminates (code 78)
        # child 2 terminates (signal 5)
        self.add_zombie(45, 78)
        self.add_zombie(46, -5)
        self.running = False
        self.watcher._sig_chld()

        callback1.assert_called_once_with(45, 78, 17, 8)
        callback2.assert_called_once_with(46, -5, 1147, 18)
        self.assertTrue(m.WIFSIGNALED.called)
        self.assertTrue(m.WIFEXITED.called)
        self.assertTrue(m.WEXITSTATUS.called)
        self.assertTrue(m.WTERMSIG.called)

        m.WIFSIGNALED.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WTERMSIG.reset_mock()
        m.WEXITSTATUS.reset_mock()
        callback1.reset_mock()
        callback2.reset_mock()

        # ensure that the children are effectively reaped
        self.add_zombie(45, 14)
        self.add_zombie(46, 15)
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WTERMSIG.called)

    @waitpid_mocks
    def test_sigchld_race_condition(self, m):
        # register a child
        callback = unittest.mock.Mock()

        with self.watcher:
            # child terminates before being registered
            self.add_zombie(50, 4)
            self.watcher._sig_chld()

            self.watcher.add_child_handler(50, callback, 1, 12)

        callback.assert_called_once_with(50, 4, 1, 12)
        callback.reset_mock()

        # ensure that the child is effectively reaped
        self.add_zombie(50, -1)
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback.called)

    @waitpid_mocks
    def test_sigchld_replace_handler(self, m):
        callback1 = unittest.mock.Mock()
        callback2 = unittest.mock.Mock()

        # register a child
        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(51, callback1, 19)

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # register the same child again
        with self.watcher:
            self.watcher.add_child_handler(51, callback2, 21)

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child terminates (signal 8)
        self.running = False
        self.add_zombie(51, -8)
        self.watcher._sig_chld()

        callback2.assert_called_once_with(51, -8, 21)
        self.assertFalse(callback1.called)
        self.assertTrue(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertTrue(m.WTERMSIG.called)

        m.WIFSIGNALED.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WTERMSIG.reset_mock()
        callback2.reset_mock()

        # ensure that the child is effectively reaped
        self.add_zombie(51, 13)
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(m.WTERMSIG.called)

    @waitpid_mocks
    def test_sigchld_remove_handler(self, m):
        callback = unittest.mock.Mock()

        # register a child
        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(52, callback, 1984)

        self.assertFalse(callback.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # unregister the child
        self.watcher.remove_child_handler(52)

        self.assertFalse(callback.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child terminates (code 99)
        self.running = False
        self.add_zombie(52, 99)
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback.called)

    @waitpid_mocks
    def test_sigchld_unknown_status(self, m):
        callback = unittest.mock.Mock()

        # register a child
        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(53, callback, -19)

        self.assertFalse(callback.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # terminate with unknown status
        self.zombies[53] = 1178
        self.running = False
        self.watcher._sig_chld()

        callback.assert_called_once_with(53, 1178, -19)
        self.assertTrue(m.WIFEXITED.called)
        self.assertTrue(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        callback.reset_mock()
        m.WIFEXITED.reset_mock()
        m.WIFSIGNALED.reset_mock()

        # ensure that the child is effectively reaped
        self.add_zombie(53, 101)
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback.called)

    @waitpid_mocks
    def test_remove_child_handler(self, m):
        callback1 = unittest.mock.Mock()
        callback2 = unittest.mock.Mock()
        callback3 = unittest.mock.Mock()

        # register children
        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(54, callback1, 1)
            self.watcher.add_child_handler(55, callback2, 2)
            self.watcher.add_child_handler(56, callback3, 3)

        # remove child handler 1
        self.assertTrue(self.watcher.remove_child_handler(54))

        # remove child handler 2 multiple times
        self.assertTrue(self.watcher.remove_child_handler(55))
        self.assertFalse(self.watcher.remove_child_handler(55))
        self.assertFalse(self.watcher.remove_child_handler(55))

        # all children terminate
        self.add_zombie(54, 0)
        self.add_zombie(55, 1)
        self.add_zombie(56, 2)
        self.running = False
        with self.ignore_warnings:
            self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        callback3.assert_called_once_with(56, 2, 3)

    @waitpid_mocks
    def test_sigchld_unhandled_exception(self, m):
        callback = unittest.mock.Mock()

        # register a child
        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(57, callback)

        # raise an exception
        m.waitpid.side_effect = ValueError

        with unittest.mock.patch.object(log.logger,
                                        "exception") as m_exception:

            self.assertEqual(self.watcher._sig_chld(), None)
            self.assertTrue(m_exception.called)

    @waitpid_mocks
    def test_sigchld_child_reaped_elsewhere(self, m):
        # register a child
        callback = unittest.mock.Mock()

        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(58, callback)

        self.assertFalse(callback.called)
        self.assertFalse(m.WIFEXITED.called)
        self.assertFalse(m.WIFSIGNALED.called)
        self.assertFalse(m.WEXITSTATUS.called)
        self.assertFalse(m.WTERMSIG.called)

        # child terminates
        self.running = False
        self.add_zombie(58, 4)

        # waitpid is called elsewhere
        os.waitpid(58, os.WNOHANG)

        m.waitpid.reset_mock()

        # sigchld
        with self.ignore_warnings:
            self.watcher._sig_chld()

        callback.assert_called(m.waitpid)
        if isinstance(self.watcher, asyncio.FastChildWatcher):
            # here the FastChildWatche enters a deadlock
            # (there is no way to prevent it)
            self.assertFalse(callback.called)
        else:
            callback.assert_called_once_with(58, 255)

    @waitpid_mocks
    def test_sigchld_unknown_pid_during_registration(self, m):
        # register two children
        callback1 = unittest.mock.Mock()
        callback2 = unittest.mock.Mock()

        with self.ignore_warnings, self.watcher:
            self.running = True
            # child 1 terminates
            self.add_zombie(591, 7)
            # an unknown child terminates
            self.add_zombie(593, 17)

            self.watcher._sig_chld()

            self.watcher.add_child_handler(591, callback1)
            self.watcher.add_child_handler(592, callback2)

        callback1.assert_called_once_with(591, 7)
        self.assertFalse(callback2.called)

    @waitpid_mocks
    def test_set_loop(self, m):
        # register a child
        callback = unittest.mock.Mock()

        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(60, callback)

        # attach a new loop
        old_loop = self.loop
        self.loop = test_utils.TestLoop()

        with unittest.mock.patch.object(
                old_loop,
                "remove_signal_handler") as m_old_remove_signal_handler, \
             unittest.mock.patch.object(
                self.loop,
                "add_signal_handler") as m_new_add_signal_handler:

            self.watcher.attach_loop(self.loop)

            m_old_remove_signal_handler.assert_called_once_with(
                signal.SIGCHLD)
            m_new_add_signal_handler.assert_called_once_with(
                signal.SIGCHLD, self.watcher._sig_chld)

        # child terminates
        self.running = False
        self.add_zombie(60, 9)
        self.watcher._sig_chld()

        callback.assert_called_once_with(60, 9)

    @waitpid_mocks
    def test_set_loop_race_condition(self, m):
        # register 3 children
        callback1 = unittest.mock.Mock()
        callback2 = unittest.mock.Mock()
        callback3 = unittest.mock.Mock()

        with self.watcher:
            self.running = True
            self.watcher.add_child_handler(61, callback1)
            self.watcher.add_child_handler(62, callback2)
            self.watcher.add_child_handler(622, callback3)

        # detach the loop
        old_loop = self.loop
        self.loop = None

        with unittest.mock.patch.object(
                old_loop, "remove_signal_handler") as m_remove_signal_handler:

            self.watcher.attach_loop(None)

            m_remove_signal_handler.assert_called_once_with(
                signal.SIGCHLD)

        # child 1 & 2 terminate
        self.add_zombie(61, 11)
        self.add_zombie(62, -5)

        # SIGCHLD was not catched
        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        self.assertFalse(callback3.called)

        # attach a new loop
        self.loop = test_utils.TestLoop()

        with unittest.mock.patch.object(
                self.loop, "add_signal_handler") as m_add_signal_handler:

            self.watcher.attach_loop(self.loop)

            m_add_signal_handler.assert_called_once_with(
                signal.SIGCHLD, self.watcher._sig_chld)
            callback1.assert_called_once_with(61, 11)  # race condition!
            callback2.assert_called_once_with(62, -5)  # race condition!
            self.assertFalse(callback3.called)

        callback1.reset_mock()
        callback2.reset_mock()

        # child 3 terminates
        self.running = False
        self.add_zombie(622, 19)
        self.watcher._sig_chld()

        self.assertFalse(callback1.called)
        self.assertFalse(callback2.called)
        callback3.assert_called_once_with(622, 19)

    @waitpid_mocks
    def test_close(self, m):
        # register two children
        callback1 = unittest.mock.Mock()
        callback2 = unittest.mock.Mock()

        with self.watcher:
            self.running = True
            # child 1 terminates
            self.add_zombie(63, 9)
            # other child terminates
            self.add_zombie(65, 18)
            self.watcher._sig_chld()

            self.watcher.add_child_handler(63, callback1)
            self.watcher.add_child_handler(64, callback1)

            self.assertEqual(len(self.watcher._callbacks), 1)
            if isinstance(self.watcher, asyncio.FastChildWatcher):
                self.assertEqual(len(self.watcher._zombies), 1)

            with unittest.mock.patch.object(
                    self.loop,
                    "remove_signal_handler") as m_remove_signal_handler:

                self.watcher.close()

                m_remove_signal_handler.assert_called_once_with(
                    signal.SIGCHLD)
                self.assertFalse(self.watcher._callbacks)
                if isinstance(self.watcher, asyncio.FastChildWatcher):
                    self.assertFalse(self.watcher._zombies)


class SafeChildWatcherTests (ChildWatcherTestsMixin, unittest.TestCase):
    def create_watcher(self):
        return asyncio.SafeChildWatcher()


class FastChildWatcherTests (ChildWatcherTestsMixin, unittest.TestCase):
    def create_watcher(self):
        return asyncio.FastChildWatcher()


class PolicyTests(unittest.TestCase):

    def create_policy(self):
        return asyncio.DefaultEventLoopPolicy()

    def test_get_child_watcher(self):
        policy = self.create_policy()
        self.assertIsNone(policy._watcher)

        watcher = policy.get_child_watcher()
        self.assertIsInstance(watcher, asyncio.SafeChildWatcher)

        self.assertIs(policy._watcher, watcher)

        self.assertIs(watcher, policy.get_child_watcher())
        self.assertIsNone(watcher._loop)

    def test_get_child_watcher_after_set(self):
        policy = self.create_policy()
        watcher = asyncio.FastChildWatcher()

        policy.set_child_watcher(watcher)
        self.assertIs(policy._watcher, watcher)
        self.assertIs(watcher, policy.get_child_watcher())

    def test_get_child_watcher_with_mainloop_existing(self):
        policy = self.create_policy()
        loop = policy.get_event_loop()

        self.assertIsNone(policy._watcher)
        watcher = policy.get_child_watcher()

        self.assertIsInstance(watcher, asyncio.SafeChildWatcher)
        self.assertIs(watcher._loop, loop)

        loop.close()

    def test_get_child_watcher_thread(self):

        def f():
            policy.set_event_loop(policy.new_event_loop())

            self.assertIsInstance(policy.get_event_loop(),
                                  asyncio.AbstractEventLoop)
            watcher = policy.get_child_watcher()

            self.assertIsInstance(watcher, asyncio.SafeChildWatcher)
            self.assertIsNone(watcher._loop)

            policy.get_event_loop().close()

        policy = self.create_policy()

        th = threading.Thread(target=f)
        th.start()
        th.join()

    def test_child_watcher_replace_mainloop_existing(self):
        policy = self.create_policy()
        loop = policy.get_event_loop()

        watcher = policy.get_child_watcher()

        self.assertIs(watcher._loop, loop)

        new_loop = policy.new_event_loop()
        policy.set_event_loop(new_loop)

        self.assertIs(watcher._loop, new_loop)

        policy.set_event_loop(None)

        self.assertIs(watcher._loop, None)

        loop.close()
        new_loop.close()


if __name__ == '__main__':
    unittest.main()