test_tasks.py

"""Tests for tasks.py."""

import collections
import contextvars
import gc
import io
import random
import re
import sys
import traceback
import unittest
from unittest import mock
from types import GenericAlias

import asyncio
from asyncio import futures
from asyncio import tasks
from test.test_asyncio import utils as test_utils
from test import support
from test.support.script_helper import assert_python_ok


def tearDownModule():
    asyncio.set_event_loop_policy(None)


async def coroutine_function():
    pass


def format_coroutine(qualname, state, src, source_traceback, generator=False):
    if generator:
        state = '%s' % state
    else:
        state = '%s, defined' % state
    if source_traceback is not None:
        frame = source_traceback[-1]
        return ('coro=<%s() %s at %s> created at %s:%s'
                % (qualname, state, src, frame[0], frame[1]))
    else:
        return 'coro=<%s() %s at %s>' % (qualname, state, src)


def get_innermost_context(exc):
    """
    Return information about the innermost exception context in the chain.
    """
    depth = 0
    while True:
        context = exc.__context__
        if context is None:
            break

        exc = context
        depth += 1

    return (type(exc), exc.args, depth)


class Dummy:

    def __repr__(self):
        return '<Dummy>'

    def __call__(self, *args):
        pass


class CoroLikeObject:
    def send(self, v):
        raise StopIteration(42)

    def throw(self, *exc):
        pass

    def close(self):
        pass

    def __await__(self):
        return self


class BaseTaskTests:

    Task = None
    Future = None

    def new_task(self, loop, coro, name='TestTask', context=None):
        return self.__class__.Task(coro, loop=loop, name=name, context=context)

    def new_future(self, loop):
        return self.__class__.Future(loop=loop)

    def setUp(self):
        super().setUp()
        self.loop = self.new_test_loop()
        self.loop.set_task_factory(self.new_task)
        self.loop.create_future = lambda: self.new_future(self.loop)

    def test_generic_alias(self):
        task = self.__class__.Task[str]
        self.assertEqual(task.__args__, (str,))
        self.assertIsInstance(task, GenericAlias)

    def test_task_cancel_message_getter(self):
        async def coro():
            pass
        t = self.new_task(self.loop, coro())
        self.assertTrue(hasattr(t, '_cancel_message'))
        self.assertEqual(t._cancel_message, None)

        with self.assertWarnsRegex(
            DeprecationWarning,
            "Passing 'msg' argument"
        ):
            t.cancel('my message')
        self.assertEqual(t._cancel_message, 'my message')

        with self.assertRaises(asyncio.CancelledError) as cm:
            self.loop.run_until_complete(t)

        self.assertEqual('my message', cm.exception.args[0])

    def test_task_cancel_message_setter(self):
        async def coro():
            pass
        t = self.new_task(self.loop, coro())
        with self.assertWarnsRegex(
            DeprecationWarning,
            "Passing 'msg' argument"
        ):
            t.cancel('my message')
        t._cancel_message = 'my new message'
        self.assertEqual(t._cancel_message, 'my new message')

        with self.assertRaises(asyncio.CancelledError) as cm:
            self.loop.run_until_complete(t)

        self.assertEqual('my new message', cm.exception.args[0])

    def test_task_del_collect(self):
        class Evil:
            def __del__(self):
                gc.collect()

        async def run():
            return Evil()

        self.loop.run_until_complete(
            asyncio.gather(*[
                self.new_task(self.loop, run()) for _ in range(100)
            ]))

    def test_other_loop_future(self):
        other_loop = asyncio.new_event_loop()
        fut = self.new_future(other_loop)

        async def run(fut):
            await fut

        try:
            with self.assertRaisesRegex(RuntimeError,
                                        r'Task .* got Future .* attached'):
                self.loop.run_until_complete(run(fut))
        finally:
            other_loop.close()

    def test_task_awaits_on_itself(self):

        async def test():
            await task

        task = asyncio.ensure_future(test(), loop=self.loop)

        with self.assertRaisesRegex(RuntimeError,
                                    'Task cannot await on itself'):
            self.loop.run_until_complete(task)

    def test_task_class(self):
        async def notmuch():
            return 'ok'
        t = self.new_task(self.loop, notmuch())
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')
        self.assertIs(t._loop, self.loop)
        self.assertIs(t.get_loop(), self.loop)

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)
        t = self.new_task(loop, notmuch())
        self.assertIs(t._loop, loop)
        loop.run_until_complete(t)
        loop.close()

    def test_ensure_future_coroutine(self):
        async def notmuch():
            return 'ok'
        t = asyncio.ensure_future(notmuch(), loop=self.loop)
        self.assertIs(t._loop, self.loop)
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')

        a = notmuch()
        self.addCleanup(a.close)
        with self.assertWarns(DeprecationWarning) as cm:
            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
                asyncio.ensure_future(a)
        self.assertEqual(cm.filename, __file__)

        async def test():
            return asyncio.ensure_future(notmuch())
        t = self.loop.run_until_complete(test())
        self.assertIs(t._loop, self.loop)
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')

        # Deprecated in 3.10
        asyncio.set_event_loop(self.loop)
        self.addCleanup(asyncio.set_event_loop, None)
        with self.assertWarns(DeprecationWarning) as cm:
            t = asyncio.ensure_future(notmuch())
        self.assertEqual(cm.filename, __file__)
        self.assertIs(t._loop, self.loop)
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')

    def test_ensure_future_future(self):
        f_orig = self.new_future(self.loop)
        f_orig.set_result('ko')

        f = asyncio.ensure_future(f_orig)
        self.loop.run_until_complete(f)
        self.assertTrue(f.done())
        self.assertEqual(f.result(), 'ko')
        self.assertIs(f, f_orig)

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        with self.assertRaises(ValueError):
            f = asyncio.ensure_future(f_orig, loop=loop)

        loop.close()

        f = asyncio.ensure_future(f_orig, loop=self.loop)
        self.assertIs(f, f_orig)

    def test_ensure_future_task(self):
        async def notmuch():
            return 'ok'
        t_orig = self.new_task(self.loop, notmuch())
        t = asyncio.ensure_future(t_orig)
        self.loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'ok')
        self.assertIs(t, t_orig)

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        with self.assertRaises(ValueError):
            t = asyncio.ensure_future(t_orig, loop=loop)

        loop.close()

        t = asyncio.ensure_future(t_orig, loop=self.loop)
        self.assertIs(t, t_orig)

    def test_ensure_future_awaitable(self):
        class Aw:
            def __init__(self, coro):
                self.coro = coro
            def __await__(self):
                return self.coro.__await__()

        async def coro():
            return 'ok'

        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)
        fut = asyncio.ensure_future(Aw(coro()), loop=loop)
        loop.run_until_complete(fut)
        self.assertEqual(fut.result(), 'ok')

    def test_ensure_future_neither(self):
        with self.assertRaises(TypeError):
            asyncio.ensure_future('ok')

    def test_ensure_future_error_msg(self):
        loop = asyncio.new_event_loop()
        f = self.new_future(self.loop)
        with self.assertRaisesRegex(ValueError, 'The future belongs to a '
                                    'different loop than the one specified as '
                                    'the loop argument'):
            asyncio.ensure_future(f, loop=loop)
        loop.close()

    def test_get_stack(self):
        T = None

        async def foo():
            await bar()

        async def bar():
            # test get_stack()
            f = T.get_stack(limit=1)
            try:
                self.assertEqual(f[0].f_code.co_name, 'foo')
            finally:
                f = None

            # test print_stack()
            file = io.StringIO()
            T.print_stack(limit=1, file=file)
            file.seek(0)
            tb = file.read()
            self.assertRegex(tb, r'foo\(\) running')

        async def runner():
            nonlocal T
            T = asyncio.ensure_future(foo(), loop=self.loop)
            await T

        self.loop.run_until_complete(runner())

    def test_task_repr(self):
        self.loop.set_debug(False)

        async def notmuch():
            return 'abc'

        # test coroutine function
        self.assertEqual(notmuch.__name__, 'notmuch')
        self.assertRegex(notmuch.__qualname__,
                         r'\w+.test_task_repr.<locals>.notmuch')
        self.assertEqual(notmuch.__module__, __name__)

        filename, lineno = test_utils.get_function_source(notmuch)
        src = "%s:%s" % (filename, lineno)

        # test coroutine object
        gen = notmuch()
        coro_qualname = 'BaseTaskTests.test_task_repr.<locals>.notmuch'
        self.assertEqual(gen.__name__, 'notmuch')
        self.assertEqual(gen.__qualname__, coro_qualname)

        # test pending Task
        t = self.new_task(self.loop, gen)
        t.add_done_callback(Dummy())

        coro = format_coroutine(coro_qualname, 'running', src,
                                t._source_traceback, generator=True)
        self.assertEqual(repr(t),
                         "<Task pending name='TestTask' %s cb=[<Dummy>()]>" % coro)

        # test cancelling Task
        t.cancel()  # Does not take immediate effect!
        self.assertEqual(repr(t),
                         "<Task cancelling name='TestTask' %s cb=[<Dummy>()]>" % coro)

        # test cancelled Task
        self.assertRaises(asyncio.CancelledError,
                          self.loop.run_until_complete, t)
        coro = format_coroutine(coro_qualname, 'done', src,
                                t._source_traceback)
        self.assertEqual(repr(t),
                         "<Task cancelled name='TestTask' %s>" % coro)

        # test finished Task
        t = self.new_task(self.loop, notmuch())
        self.loop.run_until_complete(t)
        coro = format_coroutine(coro_qualname, 'done', src,
                                t._source_traceback)
        self.assertEqual(repr(t),
                         "<Task finished name='TestTask' %s result='abc'>" % coro)

    def test_task_repr_autogenerated(self):
        async def notmuch():
            return 123

        t1 = self.new_task(self.loop, notmuch(), None)
        t2 = self.new_task(self.loop, notmuch(), None)
        self.assertNotEqual(repr(t1), repr(t2))

        match1 = re.match(r"^<Task pending name='Task-(\d+)'", repr(t1))
        self.assertIsNotNone(match1)
        match2 = re.match(r"^<Task pending name='Task-(\d+)'", repr(t2))
        self.assertIsNotNone(match2)

        # Autogenerated task names should have monotonically increasing numbers
        self.assertLess(int(match1.group(1)), int(match2.group(1)))
        self.loop.run_until_complete(t1)
        self.loop.run_until_complete(t2)

    def test_task_repr_name_not_str(self):
        async def notmuch():
            return 123

        t = self.new_task(self.loop, notmuch())
        t.set_name({6})
        self.assertEqual(t.get_name(), '{6}')
        self.loop.run_until_complete(t)

    def test_task_repr_wait_for(self):
        self.loop.set_debug(False)

        async def wait_for(fut):
            return await fut

        fut = self.new_future(self.loop)
        task = self.new_task(self.loop, wait_for(fut))
        test_utils.run_briefly(self.loop)
        self.assertRegex(repr(task),
                         '<Task .* wait_for=%s>' % re.escape(repr(fut)))

        fut.set_result(None)
        self.loop.run_until_complete(task)

    def test_task_basics(self):

        async def outer():
            a = await inner1()
            b = await inner2()
            return a+b

        async def inner1():
            return 42

        async def inner2():
            return 1000

        t = outer()
        self.assertEqual(self.loop.run_until_complete(t), 1042)

    def test_exception_chaining_after_await(self):
        # Test that when awaiting on a task when an exception is already
        # active, if the task raises an exception it will be chained
        # with the original.
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def raise_error():
            raise ValueError

        async def run():
            try:
                raise KeyError(3)
            except Exception as exc:
                task = self.new_task(loop, raise_error())
                try:
                    await task
                except Exception as exc:
                    self.assertEqual(type(exc), ValueError)
                    chained = exc.__context__
                    self.assertEqual((type(chained), chained.args),
                        (KeyError, (3,)))

        try:
            task = self.new_task(loop, run())
            loop.run_until_complete(task)
        finally:
            loop.close()

    def test_exception_chaining_after_await_with_context_cycle(self):
        # Check trying to create an exception context cycle:
        # https://bugs.python.org/issue40696
        has_cycle = None
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def process_exc(exc):
            raise exc

        async def run():
            nonlocal has_cycle
            try:
                raise KeyError('a')
            except Exception as exc:
                task = self.new_task(loop, process_exc(exc))
                try:
                    await task
                except BaseException as exc:
                    has_cycle = (exc is exc.__context__)
                    # Prevent a hang if has_cycle is True.
                    exc.__context__ = None

        try:
            task = self.new_task(loop, run())
            loop.run_until_complete(task)
        finally:
            loop.close()
        # This also distinguishes from the initial has_cycle=None.
        self.assertEqual(has_cycle, False)


    def test_cancelling(self):
        loop = asyncio.new_event_loop()

        async def task():
            await asyncio.sleep(10)

        try:
            t = self.new_task(loop, task())
            self.assertFalse(t.cancelling())
            self.assertNotIn(" cancelling ", repr(t))
            self.assertTrue(t.cancel())
            self.assertTrue(t.cancelling())
            self.assertIn(" cancelling ", repr(t))

            # Since we commented out two lines from Task.cancel(),
            # this t.cancel() call now returns True.
            # self.assertFalse(t.cancel())
            self.assertTrue(t.cancel())

            with self.assertRaises(asyncio.CancelledError):
                loop.run_until_complete(t)
        finally:
            loop.close()

    def test_uncancel(self):
        loop = asyncio.new_event_loop()

        async def task():
            try:
                await asyncio.sleep(10)
            except asyncio.CancelledError:
                asyncio.current_task().uncancel()
                await asyncio.sleep(10)

        try:
            t = self.new_task(loop, task())
            loop.run_until_complete(asyncio.sleep(0.01))

            # Cancel first sleep
            self.assertTrue(t.cancel())
            self.assertIn(" cancelling ", repr(t))
            self.assertEqual(t.cancelling(), 1)
            self.assertFalse(t.cancelled())  # Task is still not complete
            loop.run_until_complete(asyncio.sleep(0.01))

            # after .uncancel()
            self.assertNotIn(" cancelling ", repr(t))
            self.assertEqual(t.cancelling(), 0)
            self.assertFalse(t.cancelled())  # Task is still not complete

            # Cancel second sleep
            self.assertTrue(t.cancel())
            self.assertEqual(t.cancelling(), 1)
            self.assertFalse(t.cancelled())  # Task is still not complete
            with self.assertRaises(asyncio.CancelledError):
                loop.run_until_complete(t)
            self.assertTrue(t.cancelled())  # Finally, task complete
            self.assertTrue(t.done())

            # uncancel is no longer effective after the task is complete
            t.uncancel()
            self.assertTrue(t.cancelled())
            self.assertTrue(t.done())
        finally:
            loop.close()

    def test_cancel(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        async def task():
            await asyncio.sleep(10.0)
            return 12

        t = self.new_task(loop, task())
        loop.call_soon(t.cancel)
        with self.assertRaises(asyncio.CancelledError):
            loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertTrue(t.cancelled())
        self.assertFalse(t.cancel())

    def test_cancel_with_message_then_future_result(self):
        # Test Future.result() after calling cancel() with a message.
        cases = [
            ((), ()),
            ((None,), ()),
            (('my message',), ('my message',)),
            # Non-string values should roundtrip.
            ((5,), (5,)),
        ]
        for cancel_args, expected_args in cases:
            with self.subTest(cancel_args=cancel_args):
                loop = asyncio.new_event_loop()
                self.set_event_loop(loop)

                async def sleep():
                    await asyncio.sleep(10)

                async def coro():
                    task = self.new_task(loop, sleep())
                    await asyncio.sleep(0)
                    if cancel_args not in ((), (None,)):
                        with self.assertWarnsRegex(
                                DeprecationWarning,
                                "Passing 'msg' argument"
                        ):
                            task.cancel(*cancel_args)
                    else:
                        task.cancel(*cancel_args)
                    done, pending = await asyncio.wait([task])
                    task.result()

                task = self.new_task(loop, coro())
                with self.assertRaises(asyncio.CancelledError) as cm:
                    loop.run_until_complete(task)
                exc = cm.exception
                self.assertEqual(exc.args, expected_args)

                actual = get_innermost_context(exc)
                self.assertEqual(actual,
                    (asyncio.CancelledError, expected_args, 0))

    def test_cancel_with_message_then_future_exception(self):
        # Test Future.exception() after calling cancel() with a message.
        cases = [
            ((), ()),
            ((None,), ()),
            (('my message',), ('my message',)),
            # Non-string values should roundtrip.
            ((5,), (5,)),
        ]
        for cancel_args, expected_args in cases:
            with self.subTest(cancel_args=cancel_args):
                loop = asyncio.new_event_loop()
                self.set_event_loop(loop)

                async def sleep():
                    await asyncio.sleep(10)

                async def coro():
                    task = self.new_task(loop, sleep())
                    await asyncio.sleep(0)
                    if cancel_args not in ((), (None,)):
                        with self.assertWarnsRegex(
                                DeprecationWarning,
                                "Passing 'msg' argument"
                        ):
                            task.cancel(*cancel_args)
                    else:
                        task.cancel(*cancel_args)
                    done, pending = await asyncio.wait([task])
                    task.exception()

                task = self.new_task(loop, coro())
                with self.assertRaises(asyncio.CancelledError) as cm:
                    loop.run_until_complete(task)
                exc = cm.exception
                self.assertEqual(exc.args, expected_args)

                actual = get_innermost_context(exc)
                self.assertEqual(actual,
                    (asyncio.CancelledError, expected_args, 0))

    def test_cancellation_exception_context(self):
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)
        fut = loop.create_future()

        async def sleep():
            fut.set_result(None)
            await asyncio.sleep(10)

        def cancel(task, msg):
            with self.assertWarnsRegex(
                    DeprecationWarning,
                    "Passing 'msg' argument"
            ):
                task.cancel(msg)

        async def coro():
            inner_task = self.new_task(loop, sleep())
            await fut
            loop.call_soon(cancel, inner_task, 'msg')
            try:
                await inner_task
            except asyncio.CancelledError as ex:
                raise ValueError("cancelled") from ex

        task = self.new_task(loop, coro())
        with self.assertRaises(ValueError) as cm:
            loop.run_until_complete(task)
        exc = cm.exception
        self.assertEqual(exc.args, ('cancelled',))

        actual = get_innermost_context(exc)
        self.assertEqual(actual,
            (asyncio.CancelledError, ('msg',), 1))

    def test_cancel_with_message_before_starting_task(self):
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def sleep():
            await asyncio.sleep(10)

        async def coro():
            task = self.new_task(loop, sleep())
            # We deliberately leave out the sleep here.
            with self.assertWarnsRegex(
                    DeprecationWarning,
                    "Passing 'msg' argument"
            ):
                task.cancel('my message')
            done, pending = await asyncio.wait([task])
            task.exception()

        task = self.new_task(loop, coro())
        with self.assertRaises(asyncio.CancelledError) as cm:
            loop.run_until_complete(task)
        exc = cm.exception
        self.assertEqual(exc.args, ('my message',))

        actual = get_innermost_context(exc)
        self.assertEqual(actual,
            (asyncio.CancelledError, ('my message',), 0))

    def test_cancel_yield(self):
        async def task():
            await asyncio.sleep(0)
            await asyncio.sleep(0)
            return 12

        t = self.new_task(self.loop, task())
        test_utils.run_briefly(self.loop)  # start coro
        t.cancel()
        self.assertRaises(
            asyncio.CancelledError, self.loop.run_until_complete, t)
        self.assertTrue(t.done())
        self.assertTrue(t.cancelled())
        self.assertFalse(t.cancel())

    def test_cancel_inner_future(self):
        f = self.new_future(self.loop)

        async def task():
            await f
            return 12

        t = self.new_task(self.loop, task())
        test_utils.run_briefly(self.loop)  # start task
        f.cancel()
        with self.assertRaises(asyncio.CancelledError):
            self.loop.run_until_complete(t)
        self.assertTrue(f.cancelled())
        self.assertTrue(t.cancelled())

    def test_cancel_both_task_and_inner_future(self):
        f = self.new_future(self.loop)

        async def task():
            await f
            return 12

        t = self.new_task(self.loop, task())
        test_utils.run_briefly(self.loop)

        f.cancel()
        t.cancel()

        with self.assertRaises(asyncio.CancelledError):
            self.loop.run_until_complete(t)

        self.assertTrue(t.done())
        self.assertTrue(f.cancelled())
        self.assertTrue(t.cancelled())

    def test_cancel_task_catching(self):
        fut1 = self.new_future(self.loop)
        fut2 = self.new_future(self.loop)

        async def task():
            await fut1
            try:
                await fut2
            except asyncio.CancelledError:
                return 42

        t = self.new_task(self.loop, task())
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut1)  # White-box test.
        fut1.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut2)  # White-box test.
        t.cancel()
        self.assertTrue(fut2.cancelled())
        res = self.loop.run_until_complete(t)
        self.assertEqual(res, 42)
        self.assertFalse(t.cancelled())

    def test_cancel_task_ignoring(self):
        fut1 = self.new_future(self.loop)
        fut2 = self.new_future(self.loop)
        fut3 = self.new_future(self.loop)

        async def task():
            await fut1
            try:
                await fut2
            except asyncio.CancelledError:
                pass
            res = await fut3
            return res

        t = self.new_task(self.loop, task())
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut1)  # White-box test.
        fut1.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut2)  # White-box test.
        t.cancel()
        self.assertTrue(fut2.cancelled())
        test_utils.run_briefly(self.loop)
        self.assertIs(t._fut_waiter, fut3)  # White-box test.
        fut3.set_result(42)
        res = self.loop.run_until_complete(t)
        self.assertEqual(res, 42)
        self.assertFalse(fut3.cancelled())
        self.assertFalse(t.cancelled())

    def test_cancel_current_task(self):
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def task():
            t.cancel()
            self.assertTrue(t._must_cancel)  # White-box test.
            # The sleep should be cancelled immediately.
            await asyncio.sleep(100)
            return 12

        t = self.new_task(loop, task())
        self.assertFalse(t.cancelled())
        self.assertRaises(
            asyncio.CancelledError, loop.run_until_complete, t)
        self.assertTrue(t.done())
        self.assertTrue(t.cancelled())
        self.assertFalse(t._must_cancel)  # White-box test.
        self.assertFalse(t.cancel())

    def test_cancel_at_end(self):
        """coroutine end right after task is cancelled"""
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def task():
            t.cancel()
            self.assertTrue(t._must_cancel)  # White-box test.
            return 12

        t = self.new_task(loop, task())
        self.assertFalse(t.cancelled())
        self.assertRaises(
            asyncio.CancelledError, loop.run_until_complete, t)
        self.assertTrue(t.done())
        self.assertTrue(t.cancelled())
        self.assertFalse(t._must_cancel)  # White-box test.
        self.assertFalse(t.cancel())

    def test_cancel_awaited_task(self):
        # This tests for a relatively rare condition when
        # a task cancellation is requested for a task which is not
        # currently blocked, such as a task cancelling itself.
        # In this situation we must ensure that whatever next future
        # or task the cancelled task blocks on is cancelled correctly
        # as well.  See also bpo-34872.
        loop = asyncio.new_event_loop()
        self.addCleanup(lambda: loop.close())

        task = nested_task = None
        fut = self.new_future(loop)

        async def nested():
            await fut

        async def coro():
            nonlocal nested_task
            # Create a sub-task and wait for it to run.
            nested_task = self.new_task(loop, nested())
            await asyncio.sleep(0)

            # Request the current task to be cancelled.
            task.cancel()
            # Block on the nested task, which should be immediately
            # cancelled.
            await nested_task

        task = self.new_task(loop, coro())
        with self.assertRaises(asyncio.CancelledError):
            loop.run_until_complete(task)

        self.assertTrue(task.cancelled())
        self.assertTrue(nested_task.cancelled())
        self.assertTrue(fut.cancelled())

    def assert_text_contains(self, text, substr):
        if substr not in text:
            raise RuntimeError(f'text {substr!r} not found in:\n>>>{text}<<<')

    def test_cancel_traceback_for_future_result(self):
        # When calling Future.result() on a cancelled task, check that the
        # line of code that was interrupted is included in the traceback.
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def nested():
            # This will get cancelled immediately.
            await asyncio.sleep(10)

        async def coro():
            task = self.new_task(loop, nested())
            await asyncio.sleep(0)
            task.cancel()
            await task  # search target

        task = self.new_task(loop, coro())
        try:
            loop.run_until_complete(task)
        except asyncio.CancelledError:
            tb = traceback.format_exc()
            self.assert_text_contains(tb, "await asyncio.sleep(10)")
            # The intermediate await should also be included.
            self.assert_text_contains(tb, "await task  # search target")
        else:
            self.fail('CancelledError did not occur')

    def test_cancel_traceback_for_future_exception(self):
        # When calling Future.exception() on a cancelled task, check that the
        # line of code that was interrupted is included in the traceback.
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def nested():
            # This will get cancelled immediately.
            await asyncio.sleep(10)

        async def coro():
            task = self.new_task(loop, nested())
            await asyncio.sleep(0)
            task.cancel()
            done, pending = await asyncio.wait([task])
            task.exception()  # search target

        task = self.new_task(loop, coro())
        try:
            loop.run_until_complete(task)
        except asyncio.CancelledError:
            tb = traceback.format_exc()
            self.assert_text_contains(tb, "await asyncio.sleep(10)")
            # The intermediate await should also be included.
            self.assert_text_contains(tb,
                "task.exception()  # search target")
        else:
            self.fail('CancelledError did not occur')

    def test_stop_while_run_in_complete(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0.1
            self.assertAlmostEqual(0.2, when)
            when = yield 0.1
            self.assertAlmostEqual(0.3, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        x = 0

        async def task():
            nonlocal x
            while x < 10:
                await asyncio.sleep(0.1)
                x += 1
                if x == 2:
                    loop.stop()

        t = self.new_task(loop, task())
        with self.assertRaises(RuntimeError) as cm:
            loop.run_until_complete(t)
        self.assertEqual(str(cm.exception),
                         'Event loop stopped before Future completed.')
        self.assertFalse(t.done())
        self.assertEqual(x, 2)
        self.assertAlmostEqual(0.3, loop.time())

        t.cancel()
        self.assertRaises(asyncio.CancelledError, loop.run_until_complete, t)

    def test_log_traceback(self):
        async def coro():
            pass

        task = self.new_task(self.loop, coro())
        with self.assertRaisesRegex(ValueError, 'can only be set to False'):
            task._log_traceback = True
        self.loop.run_until_complete(task)

    def test_wait(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            yield 0.15

        loop = self.new_test_loop(gen)

        a = self.new_task(loop, asyncio.sleep(0.1))
        b = self.new_task(loop, asyncio.sleep(0.15))

        async def foo():
            done, pending = await asyncio.wait([b, a])
            self.assertEqual(done, set([a, b]))
            self.assertEqual(pending, set())
            return 42

        res = loop.run_until_complete(self.new_task(loop, foo()))
        self.assertEqual(res, 42)
        self.assertAlmostEqual(0.15, loop.time())

        # Doing it again should take no time and exercise a different path.
        res = loop.run_until_complete(self.new_task(loop, foo()))
        self.assertAlmostEqual(0.15, loop.time())
        self.assertEqual(res, 42)

    def test_wait_duplicate_coroutines(self):

        async def coro(s):
            return s
        c = self.loop.create_task(coro('test'))
        task = self.new_task(
            self.loop,
            asyncio.wait([c, c, self.loop.create_task(coro('spam'))]))

        done, pending = self.loop.run_until_complete(task)

        self.assertFalse(pending)
        self.assertEqual(set(f.result() for f in done), {'test', 'spam'})

    def test_wait_errors(self):
        self.assertRaises(
            ValueError, self.loop.run_until_complete,
            asyncio.wait(set()))

        # -1 is an invalid return_when value
        sleep_coro = asyncio.sleep(10.0)
        wait_coro = asyncio.wait([sleep_coro], return_when=-1)
        self.assertRaises(ValueError,
                          self.loop.run_until_complete, wait_coro)

        sleep_coro.close()

    def test_wait_first_completed(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            when = yield 0
            self.assertAlmostEqual(0.1, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        a = self.new_task(loop, asyncio.sleep(10.0))
        b = self.new_task(loop, asyncio.sleep(0.1))
        task = self.new_task(
            loop,
            asyncio.wait([b, a], return_when=asyncio.FIRST_COMPLETED))

        done, pending = loop.run_until_complete(task)
        self.assertEqual({b}, done)
        self.assertEqual({a}, pending)
        self.assertFalse(a.done())
        self.assertTrue(b.done())
        self.assertIsNone(b.result())
        self.assertAlmostEqual(0.1, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b]))

    def test_wait_really_done(self):
        # there is possibility that some tasks in the pending list
        # became done but their callbacks haven't all been called yet

        async def coro1():
            await asyncio.sleep(0)

        async def coro2():
            await asyncio.sleep(0)
            await asyncio.sleep(0)

        a = self.new_task(self.loop, coro1())
        b = self.new_task(self.loop, coro2())
        task = self.new_task(
            self.loop,
            asyncio.wait([b, a], return_when=asyncio.FIRST_COMPLETED))

        done, pending = self.loop.run_until_complete(task)
        self.assertEqual({a, b}, done)
        self.assertTrue(a.done())
        self.assertIsNone(a.result())
        self.assertTrue(b.done())
        self.assertIsNone(b.result())

    def test_wait_first_exception(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        # first_exception, task already has exception
        a = self.new_task(loop, asyncio.sleep(10.0))

        async def exc():
            raise ZeroDivisionError('err')

        b = self.new_task(loop, exc())
        task = self.new_task(
            loop,
            asyncio.wait([b, a], return_when=asyncio.FIRST_EXCEPTION))

        done, pending = loop.run_until_complete(task)
        self.assertEqual({b}, done)
        self.assertEqual({a}, pending)
        self.assertAlmostEqual(0, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b]))

    def test_wait_first_exception_in_wait(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            when = yield 0
            self.assertAlmostEqual(0.01, when)
            yield 0.01

        loop = self.new_test_loop(gen)

        # first_exception, exception during waiting
        a = self.new_task(loop, asyncio.sleep(10.0))

        async def exc():
            await asyncio.sleep(0.01)
            raise ZeroDivisionError('err')

        b = self.new_task(loop, exc())
        task = asyncio.wait([b, a], return_when=asyncio.FIRST_EXCEPTION)

        done, pending = loop.run_until_complete(task)
        self.assertEqual({b}, done)
        self.assertEqual({a}, pending)
        self.assertAlmostEqual(0.01, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b]))

    def test_wait_with_exception(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            yield 0.15

        loop = self.new_test_loop(gen)

        a = self.new_task(loop, asyncio.sleep(0.1))

        async def sleeper():
            await asyncio.sleep(0.15)
            raise ZeroDivisionError('really')

        b = self.new_task(loop, sleeper())

        async def foo():
            done, pending = await asyncio.wait([b, a])
            self.assertEqual(len(done), 2)
            self.assertEqual(pending, set())
            errors = set(f for f in done if f.exception() is not None)
            self.assertEqual(len(errors), 1)

        loop.run_until_complete(self.new_task(loop, foo()))
        self.assertAlmostEqual(0.15, loop.time())

        loop.run_until_complete(self.new_task(loop, foo()))
        self.assertAlmostEqual(0.15, loop.time())

    def test_wait_with_timeout(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            when = yield 0
            self.assertAlmostEqual(0.11, when)
            yield 0.11

        loop = self.new_test_loop(gen)

        a = self.new_task(loop, asyncio.sleep(0.1))
        b = self.new_task(loop, asyncio.sleep(0.15))

        async def foo():
            done, pending = await asyncio.wait([b, a], timeout=0.11)
            self.assertEqual(done, set([a]))
            self.assertEqual(pending, set([b]))

        loop.run_until_complete(self.new_task(loop, foo()))
        self.assertAlmostEqual(0.11, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b]))

    def test_wait_concurrent_complete(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            when = yield 0
            self.assertAlmostEqual(0.1, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        a = self.new_task(loop, asyncio.sleep(0.1))
        b = self.new_task(loop, asyncio.sleep(0.15))

        done, pending = loop.run_until_complete(
            asyncio.wait([b, a], timeout=0.1))

        self.assertEqual(done, set([a]))
        self.assertEqual(pending, set([b]))
        self.assertAlmostEqual(0.1, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b]))

    def test_wait_with_iterator_of_tasks(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(0.15, when)
            yield 0.15

        loop = self.new_test_loop(gen)

        a = self.new_task(loop, asyncio.sleep(0.1))
        b = self.new_task(loop, asyncio.sleep(0.15))

        async def foo():
            done, pending = await asyncio.wait(iter([b, a]))
            self.assertEqual(done, set([a, b]))
            self.assertEqual(pending, set())
            return 42

        res = loop.run_until_complete(self.new_task(loop, foo()))
        self.assertEqual(res, 42)
        self.assertAlmostEqual(0.15, loop.time())

    def test_as_completed(self):

        def gen():
            yield 0
            yield 0
            yield 0.01
            yield 0

        loop = self.new_test_loop(gen)
        # disable "slow callback" warning
        loop.slow_callback_duration = 1.0
        completed = set()
        time_shifted = False

        async def sleeper(dt, x):
            nonlocal time_shifted
            await asyncio.sleep(dt)
            completed.add(x)
            if not time_shifted and 'a' in completed and 'b' in completed:
                time_shifted = True
                loop.advance_time(0.14)
            return x

        a = sleeper(0.01, 'a')
        b = sleeper(0.01, 'b')
        c = sleeper(0.15, 'c')

        async def foo():
            values = []
            for f in asyncio.as_completed([b, c, a]):
                values.append(await f)
            return values

        res = loop.run_until_complete(self.new_task(loop, foo()))
        self.assertAlmostEqual(0.15, loop.time())
        self.assertTrue('a' in res[:2])
        self.assertTrue('b' in res[:2])
        self.assertEqual(res[2], 'c')

    def test_as_completed_with_timeout(self):

        def gen():
            yield
            yield 0
            yield 0
            yield 0.1

        loop = self.new_test_loop(gen)

        a = loop.create_task(asyncio.sleep(0.1, 'a'))
        b = loop.create_task(asyncio.sleep(0.15, 'b'))

        async def foo():
            values = []
            for f in asyncio.as_completed([a, b], timeout=0.12):
                if values:
                    loop.advance_time(0.02)
                try:
                    v = await f
                    values.append((1, v))
                except asyncio.TimeoutError as exc:
                    values.append((2, exc))
            return values

        res = loop.run_until_complete(self.new_task(loop, foo()))
        self.assertEqual(len(res), 2, res)
        self.assertEqual(res[0], (1, 'a'))
        self.assertEqual(res[1][0], 2)
        self.assertIsInstance(res[1][1], asyncio.TimeoutError)
        self.assertAlmostEqual(0.12, loop.time())

        # move forward to close generator
        loop.advance_time(10)
        loop.run_until_complete(asyncio.wait([a, b]))

    def test_as_completed_with_unused_timeout(self):

        def gen():
            yield
            yield 0
            yield 0.01

        loop = self.new_test_loop(gen)

        a = asyncio.sleep(0.01, 'a')

        async def foo():
            for f in asyncio.as_completed([a], timeout=1):
                v = await f
                self.assertEqual(v, 'a')

        loop.run_until_complete(self.new_task(loop, foo()))

    def test_as_completed_reverse_wait(self):

        def gen():
            yield 0
            yield 0.05
            yield 0

        loop = self.new_test_loop(gen)

        a = asyncio.sleep(0.05, 'a')
        b = asyncio.sleep(0.10, 'b')
        fs = {a, b}

        async def test():
            futs = list(asyncio.as_completed(fs))
            self.assertEqual(len(futs), 2)

            x = await futs[1]
            self.assertEqual(x, 'a')
            self.assertAlmostEqual(0.05, loop.time())
            loop.advance_time(0.05)
            y = await futs[0]
            self.assertEqual(y, 'b')
            self.assertAlmostEqual(0.10, loop.time())

        loop.run_until_complete(test())

    def test_as_completed_concurrent(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.05, when)
            when = yield 0
            self.assertAlmostEqual(0.05, when)
            yield 0.05

        a = asyncio.sleep(0.05, 'a')
        b = asyncio.sleep(0.05, 'b')
        fs = {a, b}

        async def test():
            futs = list(asyncio.as_completed(fs))
            self.assertEqual(len(futs), 2)
            done, pending = await asyncio.wait(
                [asyncio.ensure_future(fut) for fut in futs]
            )
            self.assertEqual(set(f.result() for f in done), {'a', 'b'})

        loop = self.new_test_loop(gen)
        loop.run_until_complete(test())

    def test_as_completed_duplicate_coroutines(self):

        async def coro(s):
            return s

        async def runner():
            result = []
            c = coro('ham')
            for f in asyncio.as_completed([c, c, coro('spam')]):
                result.append(await f)
            return result

        fut = self.new_task(self.loop, runner())
        self.loop.run_until_complete(fut)
        result = fut.result()
        self.assertEqual(set(result), {'ham', 'spam'})
        self.assertEqual(len(result), 2)

    def test_as_completed_coroutine_without_loop(self):
        async def coro():
            return 42

        a = coro()
        self.addCleanup(a.close)

        futs = asyncio.as_completed([a])
        with self.assertWarns(DeprecationWarning) as cm:
            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
                list(futs)
        self.assertEqual(cm.filename, __file__)

    def test_as_completed_coroutine_use_running_loop(self):
        loop = self.new_test_loop()

        async def coro():
            return 42

        async def test():
            futs = list(asyncio.as_completed([coro()]))
            self.assertEqual(len(futs), 1)
            self.assertEqual(await futs[0], 42)

        loop.run_until_complete(test())

    def test_sleep(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.05, when)
            when = yield 0.05
            self.assertAlmostEqual(0.1, when)
            yield 0.05

        loop = self.new_test_loop(gen)

        async def sleeper(dt, arg):
            await asyncio.sleep(dt/2)
            res = await asyncio.sleep(dt/2, arg)
            return res

        t = self.new_task(loop, sleeper(0.1, 'yeah'))
        loop.run_until_complete(t)
        self.assertTrue(t.done())
        self.assertEqual(t.result(), 'yeah')
        self.assertAlmostEqual(0.1, loop.time())

    def test_sleep_cancel(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        t = self.new_task(loop, asyncio.sleep(10.0, 'yeah'))

        handle = None
        orig_call_later = loop.call_later

        def call_later(delay, callback, *args):
            nonlocal handle
            handle = orig_call_later(delay, callback, *args)
            return handle

        loop.call_later = call_later
        test_utils.run_briefly(loop)

        self.assertFalse(handle._cancelled)

        t.cancel()
        test_utils.run_briefly(loop)
        self.assertTrue(handle._cancelled)

    def test_task_cancel_sleeping_task(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.1, when)
            when = yield 0
            self.assertAlmostEqual(5000, when)
            yield 0.1

        loop = self.new_test_loop(gen)

        async def sleep(dt):
            await asyncio.sleep(dt)

        async def doit():
            sleeper = self.new_task(loop, sleep(5000))
            loop.call_later(0.1, sleeper.cancel)
            try:
                await sleeper
            except asyncio.CancelledError:
                return 'cancelled'
            else:
                return 'slept in'

        doer = doit()
        self.assertEqual(loop.run_until_complete(doer), 'cancelled')
        self.assertAlmostEqual(0.1, loop.time())

    def test_task_cancel_waiter_future(self):
        fut = self.new_future(self.loop)

        async def coro():
            await fut

        task = self.new_task(self.loop, coro())
        test_utils.run_briefly(self.loop)
        self.assertIs(task._fut_waiter, fut)

        task.cancel()
        test_utils.run_briefly(self.loop)
        self.assertRaises(
            asyncio.CancelledError, self.loop.run_until_complete, task)
        self.assertIsNone(task._fut_waiter)
        self.assertTrue(fut.cancelled())

    def test_task_set_methods(self):
        async def notmuch():
            return 'ko'

        gen = notmuch()
        task = self.new_task(self.loop, gen)

        with self.assertRaisesRegex(RuntimeError, 'not support set_result'):
            task.set_result('ok')

        with self.assertRaisesRegex(RuntimeError, 'not support set_exception'):
            task.set_exception(ValueError())

        self.assertEqual(
            self.loop.run_until_complete(task),
            'ko')

    def test_step_result_future(self):
        # If coroutine returns future, task waits on this future.

        class Fut(asyncio.Future):
            def __init__(self, *args, **kwds):
                self.cb_added = False
                super().__init__(*args, **kwds)

            def add_done_callback(self, *args, **kwargs):
                self.cb_added = True
                super().add_done_callback(*args, **kwargs)

        fut = Fut(loop=self.loop)
        result = None

        async def wait_for_future():
            nonlocal result
            result = await fut

        t = self.new_task(self.loop, wait_for_future())
        test_utils.run_briefly(self.loop)
        self.assertTrue(fut.cb_added)

        res = object()
        fut.set_result(res)
        test_utils.run_briefly(self.loop)
        self.assertIs(res, result)
        self.assertTrue(t.done())
        self.assertIsNone(t.result())

    def test_baseexception_during_cancel(self):

        def gen():
            when = yield
            self.assertAlmostEqual(10.0, when)
            yield 0

        loop = self.new_test_loop(gen)

        async def sleeper():
            await asyncio.sleep(10)

        base_exc = SystemExit()

        async def notmutch():
            try:
                await sleeper()
            except asyncio.CancelledError:
                raise base_exc

        task = self.new_task(loop, notmutch())
        test_utils.run_briefly(loop)

        task.cancel()
        self.assertFalse(task.done())

        self.assertRaises(SystemExit, test_utils.run_briefly, loop)

        self.assertTrue(task.done())
        self.assertFalse(task.cancelled())
        self.assertIs(task.exception(), base_exc)

    def test_iscoroutinefunction(self):
        def fn():
            pass

        self.assertFalse(asyncio.iscoroutinefunction(fn))

        def fn1():
            yield
        self.assertFalse(asyncio.iscoroutinefunction(fn1))

        async def fn2():
            pass
        self.assertTrue(asyncio.iscoroutinefunction(fn2))

        self.assertFalse(asyncio.iscoroutinefunction(mock.Mock()))
        self.assertTrue(asyncio.iscoroutinefunction(mock.AsyncMock()))

    def test_coroutine_non_gen_function(self):
        async def func():
            return 'test'

        self.assertTrue(asyncio.iscoroutinefunction(func))

        coro = func()
        self.assertTrue(asyncio.iscoroutine(coro))

        res = self.loop.run_until_complete(coro)
        self.assertEqual(res, 'test')

    def test_coroutine_non_gen_function_return_future(self):
        fut = self.new_future(self.loop)

        async def func():
            return fut

        async def coro():
            fut.set_result('test')

        t1 = self.new_task(self.loop, func())
        t2 = self.new_task(self.loop, coro())
        res = self.loop.run_until_complete(t1)
        self.assertEqual(res, fut)
        self.assertIsNone(t2.result())

    def test_current_task(self):
        self.assertIsNone(asyncio.current_task(loop=self.loop))

        async def coro(loop):
            self.assertIs(asyncio.current_task(), task)

            self.assertIs(asyncio.current_task(None), task)
            self.assertIs(asyncio.current_task(), task)

        task = self.new_task(self.loop, coro(self.loop))
        self.loop.run_until_complete(task)
        self.assertIsNone(asyncio.current_task(loop=self.loop))

    def test_current_task_with_interleaving_tasks(self):
        self.assertIsNone(asyncio.current_task(loop=self.loop))

        fut1 = self.new_future(self.loop)
        fut2 = self.new_future(self.loop)

        async def coro1(loop):
            self.assertTrue(asyncio.current_task() is task1)
            await fut1
            self.assertTrue(asyncio.current_task() is task1)
            fut2.set_result(True)

        async def coro2(loop):
            self.assertTrue(asyncio.current_task() is task2)
            fut1.set_result(True)
            await fut2
            self.assertTrue(asyncio.current_task() is task2)

        task1 = self.new_task(self.loop, coro1(self.loop))
        task2 = self.new_task(self.loop, coro2(self.loop))

        self.loop.run_until_complete(asyncio.wait((task1, task2)))
        self.assertIsNone(asyncio.current_task(loop=self.loop))

    # Some thorough tests for cancellation propagation through
    # coroutines, tasks and wait().

    def test_yield_future_passes_cancel(self):
        # Cancelling outer() cancels inner() cancels waiter.
        proof = 0
        waiter = self.new_future(self.loop)

        async def inner():
            nonlocal proof
            try:
                await waiter
            except asyncio.CancelledError:
                proof += 1
                raise
            else:
                self.fail('got past sleep() in inner()')

        async def outer():
            nonlocal proof
            try:
                await inner()
            except asyncio.CancelledError:
                proof += 100  # Expect this path.
            else:
                proof += 10

        f = asyncio.ensure_future(outer(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        f.cancel()
        self.loop.run_until_complete(f)
        self.assertEqual(proof, 101)
        self.assertTrue(waiter.cancelled())

    def test_yield_wait_does_not_shield_cancel(self):
        # Cancelling outer() makes wait() return early, leaves inner()
        # running.
        proof = 0
        waiter = self.new_future(self.loop)

        async def inner():
            nonlocal proof
            await waiter
            proof += 1

        async def outer():
            nonlocal proof
            with self.assertWarns(DeprecationWarning):
                d, p = await asyncio.wait([asyncio.create_task(inner())])
            proof += 100

        f = asyncio.ensure_future(outer(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        f.cancel()
        self.assertRaises(
            asyncio.CancelledError, self.loop.run_until_complete, f)
        waiter.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertEqual(proof, 1)

    def test_shield_result(self):
        inner = self.new_future(self.loop)
        outer = asyncio.shield(inner)
        inner.set_result(42)
        res = self.loop.run_until_complete(outer)
        self.assertEqual(res, 42)

    def test_shield_exception(self):
        inner = self.new_future(self.loop)
        outer = asyncio.shield(inner)
        test_utils.run_briefly(self.loop)
        exc = RuntimeError('expected')
        inner.set_exception(exc)
        test_utils.run_briefly(self.loop)
        self.assertIs(outer.exception(), exc)

    def test_shield_cancel_inner(self):
        inner = self.new_future(self.loop)
        outer = asyncio.shield(inner)
        test_utils.run_briefly(self.loop)
        inner.cancel()
        test_utils.run_briefly(self.loop)
        self.assertTrue(outer.cancelled())

    def test_shield_cancel_outer(self):
        inner = self.new_future(self.loop)
        outer = asyncio.shield(inner)
        test_utils.run_briefly(self.loop)
        outer.cancel()
        test_utils.run_briefly(self.loop)
        self.assertTrue(outer.cancelled())
        self.assertEqual(0, 0 if outer._callbacks is None else len(outer._callbacks))

    def test_shield_shortcut(self):
        fut = self.new_future(self.loop)
        fut.set_result(42)
        res = self.loop.run_until_complete(asyncio.shield(fut))
        self.assertEqual(res, 42)

    def test_shield_effect(self):
        # Cancelling outer() does not affect inner().
        proof = 0
        waiter = self.new_future(self.loop)

        async def inner():
            nonlocal proof
            await waiter
            proof += 1

        async def outer():
            nonlocal proof
            await asyncio.shield(inner())
            proof += 100

        f = asyncio.ensure_future(outer(), loop=self.loop)
        test_utils.run_briefly(self.loop)
        f.cancel()
        with self.assertRaises(asyncio.CancelledError):
            self.loop.run_until_complete(f)
        waiter.set_result(None)
        test_utils.run_briefly(self.loop)
        self.assertEqual(proof, 1)

    def test_shield_gather(self):
        child1 = self.new_future(self.loop)
        child2 = self.new_future(self.loop)
        parent = asyncio.gather(child1, child2)
        outer = asyncio.shield(parent)
        test_utils.run_briefly(self.loop)
        outer.cancel()
        test_utils.run_briefly(self.loop)
        self.assertTrue(outer.cancelled())
        child1.set_result(1)
        child2.set_result(2)
        test_utils.run_briefly(self.loop)
        self.assertEqual(parent.result(), [1, 2])

    def test_gather_shield(self):
        child1 = self.new_future(self.loop)
        child2 = self.new_future(self.loop)
        inner1 = asyncio.shield(child1)
        inner2 = asyncio.shield(child2)
        parent = asyncio.gather(inner1, inner2)
        test_utils.run_briefly(self.loop)
        parent.cancel()
        # This should cancel inner1 and inner2 but bot child1 and child2.
        test_utils.run_briefly(self.loop)
        self.assertIsInstance(parent.exception(), asyncio.CancelledError)
        self.assertTrue(inner1.cancelled())
        self.assertTrue(inner2.cancelled())
        child1.set_result(1)
        child2.set_result(2)
        test_utils.run_briefly(self.loop)

    def test_shield_coroutine_without_loop(self):
        async def coro():
            return 42

        inner = coro()
        self.addCleanup(inner.close)
        with self.assertWarns(DeprecationWarning) as cm:
            with self.assertRaisesRegex(RuntimeError, 'There is no current event loop'):
                asyncio.shield(inner)
        self.assertEqual(cm.filename, __file__)

    def test_shield_coroutine_use_running_loop(self):
        async def coro():
            return 42

        async def test():
            return asyncio.shield(coro())
        outer = self.loop.run_until_complete(test())
        self.assertEqual(outer._loop, self.loop)
        res = self.loop.run_until_complete(outer)
        self.assertEqual(res, 42)

    def test_shield_coroutine_use_global_loop(self):
        # Deprecated in 3.10
        async def coro():
            return 42

        asyncio.set_event_loop(self.loop)
        self.addCleanup(asyncio.set_event_loop, None)
        with self.assertWarns(DeprecationWarning) as cm:
            outer = asyncio.shield(coro())
        self.assertEqual(cm.filename, __file__)
        self.assertEqual(outer._loop, self.loop)
        res = self.loop.run_until_complete(outer)
        self.assertEqual(res, 42)

    def test_as_completed_invalid_args(self):
        fut = self.new_future(self.loop)

        # as_completed() expects a list of futures, not a future instance
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.as_completed(fut))
        coro = coroutine_function()
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.as_completed(coro))
        coro.close()

    def test_wait_invalid_args(self):
        fut = self.new_future(self.loop)

        # wait() expects a list of futures, not a future instance
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.wait(fut))
        coro = coroutine_function()
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.wait(coro))
        coro.close()

        # wait() expects at least a future
        self.assertRaises(ValueError, self.loop.run_until_complete,
            asyncio.wait([]))

    def test_log_destroyed_pending_task(self):
        Task = self.__class__.Task

        async def kill_me(loop):
            future = self.new_future(loop)
            await future
            # at this point, the only reference to kill_me() task is
            # the Task._wakeup() method in future._callbacks
            raise Exception("code never reached")

        mock_handler = mock.Mock()
        self.loop.set_debug(True)
        self.loop.set_exception_handler(mock_handler)

        # schedule the task
        coro = kill_me(self.loop)
        task = asyncio.ensure_future(coro, loop=self.loop)

        self.assertEqual(asyncio.all_tasks(loop=self.loop), {task})

        asyncio.set_event_loop(None)

        # execute the task so it waits for future
        self.loop._run_once()
        self.assertEqual(len(self.loop._ready), 0)

        coro = None
        source_traceback = task._source_traceback
        task = None

        # no more reference to kill_me() task: the task is destroyed by the GC
        support.gc_collect()

        self.assertEqual(asyncio.all_tasks(loop=self.loop), set())

        mock_handler.assert_called_with(self.loop, {
            'message': 'Task was destroyed but it is pending!',
            'task': mock.ANY,
            'source_traceback': source_traceback,
        })
        mock_handler.reset_mock()

    @mock.patch('asyncio.base_events.logger')
    def test_tb_logger_not_called_after_cancel(self, m_log):
        loop = asyncio.new_event_loop()
        self.set_event_loop(loop)

        async def coro():
            raise TypeError

        async def runner():
            task = self.new_task(loop, coro())
            await asyncio.sleep(0.05)
            task.cancel()
            task = None

        loop.run_until_complete(runner())
        self.assertFalse(m_log.error.called)

    def test_task_source_traceback(self):
        self.loop.set_debug(True)

        task = self.new_task(self.loop, coroutine_function())
        lineno = sys._getframe().f_lineno - 1
        self.assertIsInstance(task._source_traceback, list)
        self.assertEqual(task._source_traceback[-2][:3],
                         (__file__,
                          lineno,
                          'test_task_source_traceback'))
        self.loop.run_until_complete(task)

    def test_cancel_gather_1(self):
        """Ensure that a gathering future refuses to be cancelled once all
        children are done"""
        loop = asyncio.new_event_loop()
        self.addCleanup(loop.close)

        fut = self.new_future(loop)
        async def create():
            # The indirection fut->child_coro is needed since otherwise the
            # gathering task is done at the same time as the child future
            def child_coro():
                return (yield from fut)
            gather_future = asyncio.gather(child_coro())
            return asyncio.ensure_future(gather_future)
        gather_task = loop.run_until_complete(create())

        cancel_result = None
        def cancelling_callback(_):
            nonlocal cancel_result
            cancel_result = gather_task.cancel()
        fut.add_done_callback(cancelling_callback)

        fut.set_result(42) # calls the cancelling_callback after fut is done()

        # At this point the task should complete.
        loop.run_until_complete(gather_task)

        # Python issue #26923: asyncio.gather drops cancellation
        self.assertEqual(cancel_result, False)
        self.assertFalse(gather_task.cancelled())
        self.assertEqual(gather_task.result(), [42])

    def test_cancel_gather_2(self):
        cases = [
            ((), ()),
            ((None,), ()),
            (('my message',), ('my message',)),
            # Non-string values should roundtrip.
            ((5,), (5,)),
        ]
        for cancel_args, expected_args in cases:
            with self.subTest(cancel_args=cancel_args):
                loop = asyncio.new_event_loop()
                self.addCleanup(loop.close)

                async def test():
                    time = 0
                    while True:
                        time += 0.05
                        await asyncio.gather(asyncio.sleep(0.05),
                                             return_exceptions=True)
                        if time > 1:
                            return

                async def main():
                    qwe = self.new_task(loop, test())
                    await asyncio.sleep(0.2)
                    if cancel_args not in ((), (None,)):
                        with self.assertWarnsRegex(
                                DeprecationWarning,
                                "Passing 'msg' argument"
                        ):
                            qwe.cancel(*cancel_args)
                    else:
                        qwe.cancel(*cancel_args)
                    await qwe

                try:
                    loop.run_until_complete(main())
                except asyncio.CancelledError as exc:
                    self.assertEqual(exc.args, expected_args)
                    actual = get_innermost_context(exc)
                    self.assertEqual(
                        actual,
                        (asyncio.CancelledError, expected_args, 0),
                    )
                else:
                    self.fail(
                        'gather() does not propagate CancelledError '
                        'raised by inner task to the gather() caller.'
                    )

    def test_exception_traceback(self):
        # See http://bugs.python.org/issue28843

        async def foo():
            1 / 0

        async def main():
            task = self.new_task(self.loop, foo())
            await asyncio.sleep(0)  # skip one loop iteration
            self.assertIsNotNone(task.exception().__traceback__)

        self.loop.run_until_complete(main())

    @mock.patch('asyncio.base_events.logger')
    def test_error_in_call_soon(self, m_log):
        def call_soon(callback, *args, **kwargs):
            raise ValueError
        self.loop.call_soon = call_soon

        async def coro():
            pass

        self.assertFalse(m_log.error.called)

        with self.assertRaises(ValueError):
            gen = coro()
            try:
                self.new_task(self.loop, gen)
            finally:
                gen.close()
        gc.collect()  # For PyPy or other GCs.

        self.assertTrue(m_log.error.called)
        message = m_log.error.call_args[0][0]
        self.assertIn('Task was destroyed but it is pending', message)

        self.assertEqual(asyncio.all_tasks(self.loop), set())

    def test_create_task_with_noncoroutine(self):
        with self.assertRaisesRegex(TypeError,
                                    "a coroutine was expected, got 123"):
            self.new_task(self.loop, 123)

        # test it for the second time to ensure that caching
        # in asyncio.iscoroutine() doesn't break things.
        with self.assertRaisesRegex(TypeError,
                                    "a coroutine was expected, got 123"):
            self.new_task(self.loop, 123)

    def test_create_task_with_async_function(self):

        async def coro():
            pass

        task = self.new_task(self.loop, coro())
        self.assertIsInstance(task, self.Task)
        self.loop.run_until_complete(task)

        # test it for the second time to ensure that caching
        # in asyncio.iscoroutine() doesn't break things.
        task = self.new_task(self.loop, coro())
        self.assertIsInstance(task, self.Task)
        self.loop.run_until_complete(task)

    def test_create_task_with_asynclike_function(self):
        task = self.new_task(self.loop, CoroLikeObject())
        self.assertIsInstance(task, self.Task)
        self.assertEqual(self.loop.run_until_complete(task), 42)

        # test it for the second time to ensure that caching
        # in asyncio.iscoroutine() doesn't break things.
        task = self.new_task(self.loop, CoroLikeObject())
        self.assertIsInstance(task, self.Task)
        self.assertEqual(self.loop.run_until_complete(task), 42)

    def test_bare_create_task(self):

        async def inner():
            return 1

        async def coro():
            task = asyncio.create_task(inner())
            self.assertIsInstance(task, self.Task)
            ret = await task
            self.assertEqual(1, ret)

        self.loop.run_until_complete(coro())

    def test_bare_create_named_task(self):

        async def coro_noop():
            pass

        async def coro():
            task = asyncio.create_task(coro_noop(), name='No-op')
            self.assertEqual(task.get_name(), 'No-op')
            await task

        self.loop.run_until_complete(coro())

    def test_context_1(self):
        cvar = contextvars.ContextVar('cvar', default='nope')

        async def sub():
            await asyncio.sleep(0.01)
            self.assertEqual(cvar.get(), 'nope')
            cvar.set('something else')

        async def main():
            self.assertEqual(cvar.get(), 'nope')
            subtask = self.new_task(loop, sub())
            cvar.set('yes')
            self.assertEqual(cvar.get(), 'yes')
            await subtask
            self.assertEqual(cvar.get(), 'yes')

        loop = asyncio.new_event_loop()
        try:
            task = self.new_task(loop, main())
            loop.run_until_complete(task)
        finally:
            loop.close()

    def test_context_2(self):
        cvar = contextvars.ContextVar('cvar', default='nope')

        async def main():
            def fut_on_done(fut):
                # This change must not pollute the context
                # of the "main()" task.
                cvar.set('something else')

            self.assertEqual(cvar.get(), 'nope')

            for j in range(2):
                fut = self.new_future(loop)
                fut.add_done_callback(fut_on_done)
                cvar.set(f'yes{j}')
                loop.call_soon(fut.set_result, None)
                await fut
                self.assertEqual(cvar.get(), f'yes{j}')

                for i in range(3):
                    # Test that task passed its context to add_done_callback:
                    cvar.set(f'yes{i}-{j}')
                    await asyncio.sleep(0.001)
                    self.assertEqual(cvar.get(), f'yes{i}-{j}')

        loop = asyncio.new_event_loop()
        try:
            task = self.new_task(loop, main())
            loop.run_until_complete(task)
        finally:
            loop.close()

        self.assertEqual(cvar.get(), 'nope')

    def test_context_3(self):
        # Run 100 Tasks in parallel, each modifying cvar.

        cvar = contextvars.ContextVar('cvar', default=-1)

        async def sub(num):
            for i in range(10):
                cvar.set(num + i)
                await asyncio.sleep(random.uniform(0.001, 0.05))
                self.assertEqual(cvar.get(), num + i)

        async def main():
            tasks = []
            for i in range(100):
                task = loop.create_task(sub(random.randint(0, 10)))
                tasks.append(task)

            await asyncio.gather(*tasks)

        loop = asyncio.new_event_loop()
        try:
            loop.run_until_complete(main())
        finally:
            loop.close()

        self.assertEqual(cvar.get(), -1)

    def test_context_4(self):
        cvar = contextvars.ContextVar('cvar')

        async def coro(val):
            await asyncio.sleep(0)
            cvar.set(val)

        async def main():
            ret = []
            ctx = contextvars.copy_context()
            ret.append(ctx.get(cvar))
            t1 = self.new_task(loop, coro(1), context=ctx)
            await t1
            ret.append(ctx.get(cvar))
            t2 = self.new_task(loop, coro(2), context=ctx)
            await t2
            ret.append(ctx.get(cvar))
            return ret

        loop = asyncio.new_event_loop()
        try:
            task = self.new_task(loop, main())
            ret = loop.run_until_complete(task)
        finally:
            loop.close()

        self.assertEqual([None, 1, 2], ret)

    def test_context_5(self):
        cvar = contextvars.ContextVar('cvar')

        async def coro(val):
            await asyncio.sleep(0)
            cvar.set(val)

        async def main():
            ret = []
            ctx = contextvars.copy_context()
            ret.append(ctx.get(cvar))
            t1 = asyncio.create_task(coro(1), context=ctx)
            await t1
            ret.append(ctx.get(cvar))
            t2 = asyncio.create_task(coro(2), context=ctx)
            await t2
            ret.append(ctx.get(cvar))
            return ret

        loop = asyncio.new_event_loop()
        try:
            task = self.new_task(loop, main())
            ret = loop.run_until_complete(task)
        finally:
            loop.close()

        self.assertEqual([None, 1, 2], ret)

    def test_context_6(self):
        cvar = contextvars.ContextVar('cvar')

        async def coro(val):
            await asyncio.sleep(0)
            cvar.set(val)

        async def main():
            ret = []
            ctx = contextvars.copy_context()
            ret.append(ctx.get(cvar))
            t1 = loop.create_task(coro(1), context=ctx)
            await t1
            ret.append(ctx.get(cvar))
            t2 = loop.create_task(coro(2), context=ctx)
            await t2
            ret.append(ctx.get(cvar))
            return ret

        loop = asyncio.new_event_loop()
        try:
            task = loop.create_task(main())
            ret = loop.run_until_complete(task)
        finally:
            loop.close()

        self.assertEqual([None, 1, 2], ret)

    def test_get_coro(self):
        loop = asyncio.new_event_loop()
        coro = coroutine_function()
        try:
            task = self.new_task(loop, coro)
            loop.run_until_complete(task)
            self.assertIs(task.get_coro(), coro)
        finally:
            loop.close()


def add_subclass_tests(cls):
    BaseTask = cls.Task
    BaseFuture = cls.Future

    if BaseTask is None or BaseFuture is None:
        return cls

    class CommonFuture:
        def __init__(self, *args, **kwargs):
            self.calls = collections.defaultdict(lambda: 0)
            super().__init__(*args, **kwargs)

        def add_done_callback(self, *args, **kwargs):
            self.calls['add_done_callback'] += 1
            return super().add_done_callback(*args, **kwargs)

    class Task(CommonFuture, BaseTask):
        def __init__(self, *args, **kwargs):
            self._check_future_called = 0
            super().__init__(*args, **kwargs)

        def _check_future(self, future):
            self._check_future_called += 1
            return super()._check_future(future)

    class Future(CommonFuture, BaseFuture):
        pass

    def test_subclasses_ctask_cfuture(self):
        fut = self.Future(loop=self.loop)

        async def func():
            self.loop.call_soon(lambda: fut.set_result('spam'))
            return await fut

        task = self.Task(func(), loop=self.loop)

        result = self.loop.run_until_complete(task)

        self.assertEqual(result, 'spam')

        self.assertEqual(
            dict(task.calls),
            {'add_done_callback': 1})

        self.assertEqual(
            dict(fut.calls),
            {'add_done_callback': 1})

        self.assertEqual(1, task._check_future_called)

    # Add patched Task & Future back to the test case
    cls.Task = Task
    cls.Future = Future

    # Add an extra unit-test
    cls.test_subclasses_ctask_cfuture = test_subclasses_ctask_cfuture

    # Disable the "test_task_source_traceback" test
    # (the test is hardcoded for a particular call stack, which
    # is slightly different for Task subclasses)
    cls.test_task_source_traceback = None

    return cls


class SetMethodsTest:

    def test_set_result_causes_invalid_state(self):
        Future = type(self).Future
        self.loop.call_exception_handler = exc_handler = mock.Mock()

        async def foo():
            await asyncio.sleep(0.1)
            return 10

        coro = foo()
        task = self.new_task(self.loop, coro)
        Future.set_result(task, 'spam')

        self.assertEqual(
            self.loop.run_until_complete(task),
            'spam')

        exc_handler.assert_called_once()
        exc = exc_handler.call_args[0][0]['exception']
        with self.assertRaisesRegex(asyncio.InvalidStateError,
                                    r'step\(\): already done'):
            raise exc

        coro.close()

    def test_set_exception_causes_invalid_state(self):
        class MyExc(Exception):
            pass

        Future = type(self).Future
        self.loop.call_exception_handler = exc_handler = mock.Mock()

        async def foo():
            await asyncio.sleep(0.1)
            return 10

        coro = foo()
        task = self.new_task(self.loop, coro)
        Future.set_exception(task, MyExc())

        with self.assertRaises(MyExc):
            self.loop.run_until_complete(task)

        exc_handler.assert_called_once()
        exc = exc_handler.call_args[0][0]['exception']
        with self.assertRaisesRegex(asyncio.InvalidStateError,
                                    r'step\(\): already done'):
            raise exc

        coro.close()


@unittest.skipUnless(hasattr(futures, '_CFuture') and
                     hasattr(tasks, '_CTask'),
                     'requires the C _asyncio module')
class CTask_CFuture_Tests(BaseTaskTests, SetMethodsTest,
                          test_utils.TestCase):

    Task = getattr(tasks, '_CTask', None)
    Future = getattr(futures, '_CFuture', None)

    @support.refcount_test
    def test_refleaks_in_task___init__(self):
        gettotalrefcount = support.get_attribute(sys, 'gettotalrefcount')
        async def coro():
            pass
        task = self.new_task(self.loop, coro())
        self.loop.run_until_complete(task)
        refs_before = gettotalrefcount()
        for i in range(100):
            task.__init__(coro(), loop=self.loop)
            self.loop.run_until_complete(task)
        self.assertAlmostEqual(gettotalrefcount() - refs_before, 0, delta=10)

    def test_del__log_destroy_pending_segfault(self):
        async def coro():
            pass
        task = self.new_task(self.loop, coro())
        self.loop.run_until_complete(task)
        with self.assertRaises(AttributeError):
            del task._log_destroy_pending


@unittest.skipUnless(hasattr(futures, '_CFuture') and
                     hasattr(tasks, '_CTask'),
                     'requires the C _asyncio module')
@add_subclass_tests
class CTask_CFuture_SubclassTests(BaseTaskTests, test_utils.TestCase):

    Task = getattr(tasks, '_CTask', None)
    Future = getattr(futures, '_CFuture', None)


@unittest.skipUnless(hasattr(tasks, '_CTask'),
                     'requires the C _asyncio module')
@add_subclass_tests
class CTaskSubclass_PyFuture_Tests(BaseTaskTests, test_utils.TestCase):

    Task = getattr(tasks, '_CTask', None)
    Future = futures._PyFuture


@unittest.skipUnless(hasattr(futures, '_CFuture'),
                     'requires the C _asyncio module')
@add_subclass_tests
class PyTask_CFutureSubclass_Tests(BaseTaskTests, test_utils.TestCase):

    Future = getattr(futures, '_CFuture', None)
    Task = tasks._PyTask


@unittest.skipUnless(hasattr(tasks, '_CTask'),
                     'requires the C _asyncio module')
class CTask_PyFuture_Tests(BaseTaskTests, test_utils.TestCase):

    Task = getattr(tasks, '_CTask', None)
    Future = futures._PyFuture


@unittest.skipUnless(hasattr(futures, '_CFuture'),
                     'requires the C _asyncio module')
class PyTask_CFuture_Tests(BaseTaskTests, test_utils.TestCase):

    Task = tasks._PyTask
    Future = getattr(futures, '_CFuture', None)


class PyTask_PyFuture_Tests(BaseTaskTests, SetMethodsTest,
                            test_utils.TestCase):

    Task = tasks._PyTask
    Future = futures._PyFuture


@add_subclass_tests
class PyTask_PyFuture_SubclassTests(BaseTaskTests, test_utils.TestCase):
    Task = tasks._PyTask
    Future = futures._PyFuture


@unittest.skipUnless(hasattr(tasks, '_CTask'),
                     'requires the C _asyncio module')
class CTask_Future_Tests(test_utils.TestCase):

    def test_foobar(self):
        class Fut(asyncio.Future):
            @property
            def get_loop(self):
                raise AttributeError

        async def coro():
            await fut
            return 'spam'

        self.loop = asyncio.new_event_loop()
        try:
            fut = Fut(loop=self.loop)
            self.loop.call_later(0.1, fut.set_result, 1)
            task = self.loop.create_task(coro())
            res = self.loop.run_until_complete(task)
        finally:
            self.loop.close()

        self.assertEqual(res, 'spam')


class BaseTaskIntrospectionTests:
    _register_task = None
    _unregister_task = None
    _enter_task = None
    _leave_task = None

    def test__register_task_1(self):
        class TaskLike:
            @property
            def _loop(self):
                return loop

            def done(self):
                return False

        task = TaskLike()
        loop = mock.Mock()

        self.assertEqual(asyncio.all_tasks(loop), set())
        self._register_task(task)
        self.assertEqual(asyncio.all_tasks(loop), {task})
        self._unregister_task(task)

    def test__register_task_2(self):
        class TaskLike:
            def get_loop(self):
                return loop

            def done(self):
                return False

        task = TaskLike()
        loop = mock.Mock()

        self.assertEqual(asyncio.all_tasks(loop), set())
        self._register_task(task)
        self.assertEqual(asyncio.all_tasks(loop), {task})
        self._unregister_task(task)

    def test__register_task_3(self):
        class TaskLike:
            def get_loop(self):
                return loop

            def done(self):
                return True

        task = TaskLike()
        loop = mock.Mock()

        self.assertEqual(asyncio.all_tasks(loop), set())
        self._register_task(task)
        self.assertEqual(asyncio.all_tasks(loop), set())
        self._unregister_task(task)

    def test__enter_task(self):
        task = mock.Mock()
        loop = mock.Mock()
        self.assertIsNone(asyncio.current_task(loop))
        self._enter_task(loop, task)
        self.assertIs(asyncio.current_task(loop), task)
        self._leave_task(loop, task)

    def test__enter_task_failure(self):
        task1 = mock.Mock()
        task2 = mock.Mock()
        loop = mock.Mock()
        self._enter_task(loop, task1)
        with self.assertRaises(RuntimeError):
            self._enter_task(loop, task2)
        self.assertIs(asyncio.current_task(loop), task1)
        self._leave_task(loop, task1)

    def test__leave_task(self):
        task = mock.Mock()
        loop = mock.Mock()
        self._enter_task(loop, task)
        self._leave_task(loop, task)
        self.assertIsNone(asyncio.current_task(loop))

    def test__leave_task_failure1(self):
        task1 = mock.Mock()
        task2 = mock.Mock()
        loop = mock.Mock()
        self._enter_task(loop, task1)
        with self.assertRaises(RuntimeError):
            self._leave_task(loop, task2)
        self.assertIs(asyncio.current_task(loop), task1)
        self._leave_task(loop, task1)

    def test__leave_task_failure2(self):
        task = mock.Mock()
        loop = mock.Mock()
        with self.assertRaises(RuntimeError):
            self._leave_task(loop, task)
        self.assertIsNone(asyncio.current_task(loop))

    def test__unregister_task(self):
        task = mock.Mock()
        loop = mock.Mock()
        task.get_loop = lambda: loop
        self._register_task(task)
        self._unregister_task(task)
        self.assertEqual(asyncio.all_tasks(loop), set())

    def test__unregister_task_not_registered(self):
        task = mock.Mock()
        loop = mock.Mock()
        self._unregister_task(task)
        self.assertEqual(asyncio.all_tasks(loop), set())


class PyIntrospectionTests(test_utils.TestCase, BaseTaskIntrospectionTests):
    _register_task = staticmethod(tasks._py_register_task)
    _unregister_task = staticmethod(tasks._py_unregister_task)
    _enter_task = staticmethod(tasks._py_enter_task)
    _leave_task = staticmethod(tasks._py_leave_task)


@unittest.skipUnless(hasattr(tasks, '_c_register_task'),
                     'requires the C _asyncio module')
class CIntrospectionTests(test_utils.TestCase, BaseTaskIntrospectionTests):
    if hasattr(tasks, '_c_register_task'):
        _register_task = staticmethod(tasks._c_register_task)
        _unregister_task = staticmethod(tasks._c_unregister_task)
        _enter_task = staticmethod(tasks._c_enter_task)
        _leave_task = staticmethod(tasks._c_leave_task)
    else:
        _register_task = _unregister_task = _enter_task = _leave_task = None


class BaseCurrentLoopTests:

    def setUp(self):
        super().setUp()
        self.loop = asyncio.new_event_loop()
        self.set_event_loop(self.loop)

    def new_task(self, coro):
        raise NotImplementedError

    def test_current_task_no_running_loop(self):
        self.assertIsNone(asyncio.current_task(loop=self.loop))

    def test_current_task_no_running_loop_implicit(self):
        with self.assertRaises(RuntimeError):
            asyncio.current_task()

    def test_current_task_with_implicit_loop(self):
        async def coro():
            self.assertIs(asyncio.current_task(loop=self.loop), task)

            self.assertIs(asyncio.current_task(None), task)
            self.assertIs(asyncio.current_task(), task)

        task = self.new_task(coro())
        self.loop.run_until_complete(task)
        self.assertIsNone(asyncio.current_task(loop=self.loop))


class PyCurrentLoopTests(BaseCurrentLoopTests, test_utils.TestCase):

    def new_task(self, coro):
        return tasks._PyTask(coro, loop=self.loop)


@unittest.skipUnless(hasattr(tasks, '_CTask'),
                     'requires the C _asyncio module')
class CCurrentLoopTests(BaseCurrentLoopTests, test_utils.TestCase):

    def new_task(self, coro):
        return getattr(tasks, '_CTask')(coro, loop=self.loop)


class GenericTaskTests(test_utils.TestCase):

    def test_future_subclass(self):
        self.assertTrue(issubclass(asyncio.Task, asyncio.Future))

    @support.cpython_only
    def test_asyncio_module_compiled(self):
        # Because of circular imports it's easy to make _asyncio
        # module non-importable.  This is a simple test that will
        # fail on systems where C modules were successfully compiled
        # (hence the test for _functools etc), but _asyncio somehow didn't.
        try:
            import _functools
            import _json
            import _pickle
        except ImportError:
            self.skipTest('C modules are not available')
        else:
            try:
                import _asyncio
            except ImportError:
                self.fail('_asyncio module is missing')


class GatherTestsBase:

    def setUp(self):
        super().setUp()
        self.one_loop = self.new_test_loop()
        self.other_loop = self.new_test_loop()
        self.set_event_loop(self.one_loop, cleanup=False)

    def _run_loop(self, loop):
        while loop._ready:
            test_utils.run_briefly(loop)

    def _check_success(self, **kwargs):
        a, b, c = [self.one_loop.create_future() for i in range(3)]
        fut = self._gather(*self.wrap_futures(a, b, c), **kwargs)
        cb = test_utils.MockCallback()
        fut.add_done_callback(cb)
        b.set_result(1)
        a.set_result(2)
        self._run_loop(self.one_loop)
        self.assertEqual(cb.called, False)
        self.assertFalse(fut.done())
        c.set_result(3)
        self._run_loop(self.one_loop)
        cb.assert_called_once_with(fut)
        self.assertEqual(fut.result(), [2, 1, 3])

    def test_success(self):
        self._check_success()
        self._check_success(return_exceptions=False)

    def test_result_exception_success(self):
        self._check_success(return_exceptions=True)

    def test_one_exception(self):
        a, b, c, d, e = [self.one_loop.create_future() for i in range(5)]
        fut = self._gather(*self.wrap_futures(a, b, c, d, e))
        cb = test_utils.MockCallback()
        fut.add_done_callback(cb)
        exc = ZeroDivisionError()
        a.set_result(1)
        b.set_exception(exc)
        self._run_loop(self.one_loop)
        self.assertTrue(fut.done())
        cb.assert_called_once_with(fut)
        self.assertIs(fut.exception(), exc)
        # Does nothing
        c.set_result(3)
        d.cancel()
        e.set_exception(RuntimeError())
        e.exception()

    def test_return_exceptions(self):
        a, b, c, d = [self.one_loop.create_future() for i in range(4)]
        fut = self._gather(*self.wrap_futures(a, b, c, d),
                           return_exceptions=True)
        cb = test_utils.MockCallback()
        fut.add_done_callback(cb)
        exc = ZeroDivisionError()
        exc2 = RuntimeError()
        b.set_result(1)
        c.set_exception(exc)
        a.set_result(3)
        self._run_loop(self.one_loop)
        self.assertFalse(fut.done())
        d.set_exception(exc2)
        self._run_loop(self.one_loop)
        self.assertTrue(fut.done())
        cb.assert_called_once_with(fut)
        self.assertEqual(fut.result(), [3, 1, exc, exc2])

    def test_env_var_debug(self):
        code = '\n'.join((
            'import asyncio.coroutines',
            'print(asyncio.coroutines._is_debug_mode())'))

        # Test with -E to not fail if the unit test was run with
        # PYTHONASYNCIODEBUG set to a non-empty string
        sts, stdout, stderr = assert_python_ok('-E', '-c', code)
        self.assertEqual(stdout.rstrip(), b'False')

        sts, stdout, stderr = assert_python_ok('-c', code,
                                               PYTHONASYNCIODEBUG='',
                                               PYTHONDEVMODE='')
        self.assertEqual(stdout.rstrip(), b'False')

        sts, stdout, stderr = assert_python_ok('-c', code,
                                               PYTHONASYNCIODEBUG='1',
                                               PYTHONDEVMODE='')
        self.assertEqual(stdout.rstrip(), b'True')

        sts, stdout, stderr = assert_python_ok('-E', '-c', code,
                                               PYTHONASYNCIODEBUG='1',
                                               PYTHONDEVMODE='')
        self.assertEqual(stdout.rstrip(), b'False')

        # -X dev
        sts, stdout, stderr = assert_python_ok('-E', '-X', 'dev',
                                               '-c', code)
        self.assertEqual(stdout.rstrip(), b'True')


class FutureGatherTests(GatherTestsBase, test_utils.TestCase):

    def wrap_futures(self, *futures):
        return futures

    def _gather(self, *args, **kwargs):
        return asyncio.gather(*args, **kwargs)

    def test_constructor_empty_sequence_without_loop(self):
        with self.assertWarns(DeprecationWarning) as cm:
            with self.assertRaises(RuntimeError):
                asyncio.gather()
        self.assertEqual(cm.filename, __file__)

    def test_constructor_empty_sequence_use_running_loop(self):
        async def gather():
            return asyncio.gather()
        fut = self.one_loop.run_until_complete(gather())
        self.assertIsInstance(fut, asyncio.Future)
        self.assertIs(fut._loop, self.one_loop)
        self._run_loop(self.one_loop)
        self.assertTrue(fut.done())
        self.assertEqual(fut.result(), [])

    def test_constructor_empty_sequence_use_global_loop(self):
        # Deprecated in 3.10
        asyncio.set_event_loop(self.one_loop)
        self.addCleanup(asyncio.set_event_loop, None)
        with self.assertWarns(DeprecationWarning) as cm:
            fut = asyncio.gather()
        self.assertEqual(cm.filename, __file__)
        self.assertIsInstance(fut, asyncio.Future)
        self.assertIs(fut._loop, self.one_loop)
        self._run_loop(self.one_loop)
        self.assertTrue(fut.done())
        self.assertEqual(fut.result(), [])

    def test_constructor_heterogenous_futures(self):
        fut1 = self.one_loop.create_future()
        fut2 = self.other_loop.create_future()
        with self.assertRaises(ValueError):
            asyncio.gather(fut1, fut2)

    def test_constructor_homogenous_futures(self):
        children = [self.other_loop.create_future() for i in range(3)]
        fut = asyncio.gather(*children)
        self.assertIs(fut._loop, self.other_loop)
        self._run_loop(self.other_loop)
        self.assertFalse(fut.done())
        fut = asyncio.gather(*children)
        self.assertIs(fut._loop, self.other_loop)
        self._run_loop(self.other_loop)
        self.assertFalse(fut.done())

    def test_one_cancellation(self):
        a, b, c, d, e = [self.one_loop.create_future() for i in range(5)]
        fut = asyncio.gather(a, b, c, d, e)
        cb = test_utils.MockCallback()
        fut.add_done_callback(cb)
        a.set_result(1)
        b.cancel()
        self._run_loop(self.one_loop)
        self.assertTrue(fut.done())
        cb.assert_called_once_with(fut)
        self.assertFalse(fut.cancelled())
        self.assertIsInstance(fut.exception(), asyncio.CancelledError)
        # Does nothing
        c.set_result(3)
        d.cancel()
        e.set_exception(RuntimeError())
        e.exception()

    def test_result_exception_one_cancellation(self):
        a, b, c, d, e, f = [self.one_loop.create_future()
                            for i in range(6)]
        fut = asyncio.gather(a, b, c, d, e, f, return_exceptions=True)
        cb = test_utils.MockCallback()
        fut.add_done_callback(cb)
        a.set_result(1)
        zde = ZeroDivisionError()
        b.set_exception(zde)
        c.cancel()
        self._run_loop(self.one_loop)
        self.assertFalse(fut.done())
        d.set_result(3)
        e.cancel()
        rte = RuntimeError()
        f.set_exception(rte)
        res = self.one_loop.run_until_complete(fut)
        self.assertIsInstance(res[2], asyncio.CancelledError)
        self.assertIsInstance(res[4], asyncio.CancelledError)
        res[2] = res[4] = None
        self.assertEqual(res, [1, zde, None, 3, None, rte])
        cb.assert_called_once_with(fut)


class CoroutineGatherTests(GatherTestsBase, test_utils.TestCase):

    def wrap_futures(self, *futures):
        coros = []
        for fut in futures:
            async def coro(fut=fut):
                return await fut
            coros.append(coro())
        return coros

    def _gather(self, *args, **kwargs):
        async def coro():
            return asyncio.gather(*args, **kwargs)
        return self.one_loop.run_until_complete(coro())

    def test_constructor_without_loop(self):
        async def coro():
            return 'abc'
        gen1 = coro()
        self.addCleanup(gen1.close)
        gen2 = coro()
        self.addCleanup(gen2.close)
        with self.assertWarns(DeprecationWarning) as cm:
            with self.assertRaises(RuntimeError):
                asyncio.gather(gen1, gen2)
        self.assertEqual(cm.filename, __file__)

    def test_constructor_use_running_loop(self):
        async def coro():
            return 'abc'
        gen1 = coro()
        gen2 = coro()
        async def gather():
            return asyncio.gather(gen1, gen2)
        fut = self.one_loop.run_until_complete(gather())
        self.assertIs(fut._loop, self.one_loop)
        self.one_loop.run_until_complete(fut)

    def test_constructor_use_global_loop(self):
        # Deprecated in 3.10
        async def coro():
            return 'abc'
        asyncio.set_event_loop(self.other_loop)
        self.addCleanup(asyncio.set_event_loop, None)
        gen1 = coro()
        gen2 = coro()
        with self.assertWarns(DeprecationWarning) as cm:
            fut = asyncio.gather(gen1, gen2)
        self.assertEqual(cm.filename, __file__)
        self.assertIs(fut._loop, self.other_loop)
        self.other_loop.run_until_complete(fut)

    def test_duplicate_coroutines(self):
        async def coro(s):
            return s
        c = coro('abc')
        fut = self._gather(c, c, coro('def'), c)
        self._run_loop(self.one_loop)
        self.assertEqual(fut.result(), ['abc', 'abc', 'def', 'abc'])

    def test_cancellation_broadcast(self):
        # Cancelling outer() cancels all children.
        proof = 0
        waiter = self.one_loop.create_future()

        async def inner():
            nonlocal proof
            await waiter
            proof += 1

        child1 = asyncio.ensure_future(inner(), loop=self.one_loop)
        child2 = asyncio.ensure_future(inner(), loop=self.one_loop)
        gatherer = None

        async def outer():
            nonlocal proof, gatherer
            gatherer = asyncio.gather(child1, child2)
            await gatherer
            proof += 100

        f = asyncio.ensure_future(outer(), loop=self.one_loop)
        test_utils.run_briefly(self.one_loop)
        self.assertTrue(f.cancel())
        with self.assertRaises(asyncio.CancelledError):
            self.one_loop.run_until_complete(f)
        self.assertFalse(gatherer.cancel())
        self.assertTrue(waiter.cancelled())
        self.assertTrue(child1.cancelled())
        self.assertTrue(child2.cancelled())
        test_utils.run_briefly(self.one_loop)
        self.assertEqual(proof, 0)

    def test_exception_marking(self):
        # Test for the first line marked "Mark exception retrieved."

        async def inner(f):
            await f
            raise RuntimeError('should not be ignored')

        a = self.one_loop.create_future()
        b = self.one_loop.create_future()

        async def outer():
            await asyncio.gather(inner(a), inner(b))

        f = asyncio.ensure_future(outer(), loop=self.one_loop)
        test_utils.run_briefly(self.one_loop)
        a.set_result(None)
        test_utils.run_briefly(self.one_loop)
        b.set_result(None)
        test_utils.run_briefly(self.one_loop)
        self.assertIsInstance(f.exception(), RuntimeError)

    def test_issue46672(self):
        with mock.patch(
            'asyncio.base_events.BaseEventLoop.call_exception_handler',
        ):
            async def coro(s):
                return s
            c = coro('abc')

            with self.assertRaises(TypeError):
                self._gather(c, {})
            self._run_loop(self.one_loop)
            # NameError should not happen:
            self.one_loop.call_exception_handler.assert_not_called()


class RunCoroutineThreadsafeTests(test_utils.TestCase):
    """Test case for asyncio.run_coroutine_threadsafe."""

    def setUp(self):
        super().setUp()
        self.loop = asyncio.new_event_loop()
        self.set_event_loop(self.loop) # Will cleanup properly

    async def add(self, a, b, fail=False, cancel=False):
        """Wait 0.05 second and return a + b."""
        await asyncio.sleep(0.05)
        if fail:
            raise RuntimeError("Fail!")
        if cancel:
            asyncio.current_task(self.loop).cancel()
            await asyncio.sleep(0)
        return a + b

    def target(self, fail=False, cancel=False, timeout=None,
               advance_coro=False):
        """Run add coroutine in the event loop."""
        coro = self.add(1, 2, fail=fail, cancel=cancel)
        future = asyncio.run_coroutine_threadsafe(coro, self.loop)
        if advance_coro:
            # this is for test_run_coroutine_threadsafe_task_factory_exception;
            # otherwise it spills errors and breaks **other** unittests, since
            # 'target' is interacting with threads.

            # With this call, `coro` will be advanced.
            self.loop.call_soon_threadsafe(coro.send, None)
        try:
            return future.result(timeout)
        finally:
            future.done() or future.cancel()

    def test_run_coroutine_threadsafe(self):
        """Test coroutine submission from a thread to an event loop."""
        future = self.loop.run_in_executor(None, self.target)
        result = self.loop.run_until_complete(future)
        self.assertEqual(result, 3)

    def test_run_coroutine_threadsafe_with_exception(self):
        """Test coroutine submission from a thread to an event loop
        when an exception is raised."""
        future = self.loop.run_in_executor(None, self.target, True)
        with self.assertRaises(RuntimeError) as exc_context:
            self.loop.run_until_complete(future)
        self.assertIn("Fail!", exc_context.exception.args)

    def test_run_coroutine_threadsafe_with_timeout(self):
        """Test coroutine submission from a thread to an event loop
        when a timeout is raised."""
        callback = lambda: self.target(timeout=0)
        future = self.loop.run_in_executor(None, callback)
        with self.assertRaises(asyncio.TimeoutError):
            self.loop.run_until_complete(future)
        test_utils.run_briefly(self.loop)
        # Check that there's no pending task (add has been cancelled)
        for task in asyncio.all_tasks(self.loop):
            self.assertTrue(task.done())

    def test_run_coroutine_threadsafe_task_cancelled(self):
        """Test coroutine submission from a thread to an event loop
        when the task is cancelled."""
        callback = lambda: self.target(cancel=True)
        future = self.loop.run_in_executor(None, callback)
        with self.assertRaises(asyncio.CancelledError):
            self.loop.run_until_complete(future)

    def test_run_coroutine_threadsafe_task_factory_exception(self):
        """Test coroutine submission from a thread to an event loop
        when the task factory raise an exception."""

        def task_factory(loop, coro):
            raise NameError

        run = self.loop.run_in_executor(
            None, lambda: self.target(advance_coro=True))

        # Set exception handler
        callback = test_utils.MockCallback()
        self.loop.set_exception_handler(callback)

        # Set corrupted task factory
        self.addCleanup(self.loop.set_task_factory,
                        self.loop.get_task_factory())
        self.loop.set_task_factory(task_factory)

        # Run event loop
        with self.assertRaises(NameError) as exc_context:
            self.loop.run_until_complete(run)

        # Check exceptions
        self.assertEqual(len(callback.call_args_list), 1)
        (loop, context), kwargs = callback.call_args
        self.assertEqual(context['exception'], exc_context.exception)


class SleepTests(test_utils.TestCase):
    def setUp(self):
        super().setUp()
        self.loop = asyncio.new_event_loop()
        self.set_event_loop(self.loop)

    def tearDown(self):
        self.loop.close()
        self.loop = None
        super().tearDown()

    def test_sleep_zero(self):
        result = 0

        def inc_result(num):
            nonlocal result
            result += num

        async def coro():
            self.loop.call_soon(inc_result, 1)
            self.assertEqual(result, 0)
            num = await asyncio.sleep(0, result=10)
            self.assertEqual(result, 1) # inc'ed by call_soon
            inc_result(num) # num should be 11

        self.loop.run_until_complete(coro())
        self.assertEqual(result, 11)


class CompatibilityTests(test_utils.TestCase):
    # Tests for checking a bridge between old-styled coroutines
    # and async/await syntax

    def setUp(self):
        super().setUp()
        self.loop = asyncio.new_event_loop()
        self.set_event_loop(self.loop)

    def tearDown(self):
        self.loop.close()
        self.loop = None
        super().tearDown()


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