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

import collections
import contextlib
import functools
import io
import os
import re
import sys
import types
import unittest
import weakref
from unittest import mock

import asyncio
from asyncio import coroutines
from asyncio import futures
from asyncio import tasks
from asyncio import test_utils
try:
    from test import support
except ImportError:
    from asyncio import test_support as support
try:
    from test.support.script_helper import assert_python_ok
except ImportError:
    try:
        from test.script_helper import assert_python_ok
    except ImportError:
        from asyncio.test_support import assert_python_ok


PY34 = (sys.version_info >= (3, 4))
PY35 = (sys.version_info >= (3, 5))


@asyncio.coroutine
def coroutine_function():
    pass


@contextlib.contextmanager
def set_coroutine_debug(enabled):
    coroutines = asyncio.coroutines

    old_debug = coroutines._DEBUG
    try:
        coroutines._DEBUG = enabled
        yield
    finally:
        coroutines._DEBUG = old_debug



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)


class Dummy:

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

    def __call__(self, *args):
        pass


class BaseTaskTests:

    Task = None
    Future = None

    def new_task(self, loop, coro):
        return self.__class__.Task(coro, loop=loop)

    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_other_loop_future(self):
        other_loop = asyncio.new_event_loop()
        fut = self.new_future(other_loop)

        @asyncio.coroutine
        def run(fut):
            yield from 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):
        @asyncio.coroutine
        def test():
            yield from 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):
        @asyncio.coroutine
        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)

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

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

    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):
        @asyncio.coroutine
        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)

    @unittest.skipUnless(PY35, 'need python 3.5 or later')
    def test_ensure_future_awaitable(self):
        class Aw:
            def __init__(self, coro):
                self.coro = coro
            def __await__(self):
                return (yield from self.coro)

        @asyncio.coroutine
        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)
        assert fut.result() == 'ok'

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

    def test_async_warning(self):
        f = self.new_future(self.loop)
        with self.assertWarnsRegex(DeprecationWarning,
                                   'function is deprecated, use ensure_'):
            self.assertIs(f, asyncio.async(f))

    def test_get_stack(self):
        T = None

        @asyncio.coroutine
        def foo():
            yield from bar()

        @asyncio.coroutine
        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')

        @asyncio.coroutine
        def runner():
            nonlocal T
            T = asyncio.ensure_future(foo(), loop=self.loop)
            yield from T

        self.loop.run_until_complete(runner())

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

        @asyncio.coroutine
        def notmuch():
            yield from []
            return 'abc'

        # test coroutine function
        self.assertEqual(notmuch.__name__, 'notmuch')
        if PY35:
            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()
        if coroutines._DEBUG or PY35:
            coro_qualname = 'BaseTaskTests.test_task_repr.<locals>.notmuch'
        else:
            coro_qualname = 'notmuch'
        self.assertEqual(gen.__name__, 'notmuch')
        if PY35:
            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 %s cb=[<Dummy>()]>' % coro)

        # test cancelling Task
        t.cancel()  # Does not take immediate effect!
        self.assertEqual(repr(t),
                         '<Task cancelling %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 %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 %s result='abc'>" % coro)

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

        @asyncio.coroutine
        def notmuch():
            # notmuch() function doesn't use yield from: it will be wrapped by
            # @coroutine decorator
            return 123

        # test coroutine function
        self.assertEqual(notmuch.__name__, 'notmuch')
        if PY35:
            self.assertRegex(notmuch.__qualname__,
                             r'\w+.test_task_repr_coro_decorator'
                             r'\.<locals>\.notmuch')
        self.assertEqual(notmuch.__module__, __name__)

        # test coroutine object
        gen = notmuch()
        if coroutines._DEBUG or PY35:
            # On Python >= 3.5, generators now inherit the name of the
            # function, as expected, and have a qualified name (__qualname__
            # attribute).
            coro_name = 'notmuch'
            coro_qualname = ('BaseTaskTests.test_task_repr_coro_decorator'
                             '.<locals>.notmuch')
        else:
            # On Python < 3.5, generators inherit the name of the code, not of
            # the function. See: http://bugs.python.org/issue21205
            coro_name = coro_qualname = 'coro'
        self.assertEqual(gen.__name__, coro_name)
        if PY35:
            self.assertEqual(gen.__qualname__, coro_qualname)

        # test repr(CoroWrapper)
        if coroutines._DEBUG:
            # format the coroutine object
            if coroutines._DEBUG:
                filename, lineno = test_utils.get_function_source(notmuch)
                frame = gen._source_traceback[-1]
                coro = ('%s() running, defined at %s:%s, created at %s:%s'
                        % (coro_qualname, filename, lineno,
                           frame[0], frame[1]))
            else:
                code = gen.gi_code
                coro = ('%s() running at %s:%s'
                        % (coro_qualname, code.co_filename,
                           code.co_firstlineno))

            self.assertEqual(repr(gen), '<CoroWrapper %s>' % coro)

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

        # format the coroutine object
        if coroutines._DEBUG:
            src = '%s:%s' % test_utils.get_function_source(notmuch)
        else:
            code = gen.gi_code
            src = '%s:%s' % (code.co_filename, code.co_firstlineno)
        coro = format_coroutine(coro_qualname, 'running', src,
                                t._source_traceback,
                                generator=not coroutines._DEBUG)
        self.assertEqual(repr(t),
                         '<Task pending %s cb=[<Dummy>()]>' % coro)
        self.loop.run_until_complete(t)

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

        @asyncio.coroutine
        def wait_for(fut):
            return (yield from 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_repr_partial_corowrapper(self):
        # Issue #222: repr(CoroWrapper) must not fail in debug mode if the
        # coroutine is a partial function
        with set_coroutine_debug(True):
            self.loop.set_debug(True)

            @asyncio.coroutine
            def func(x, y):
                yield from asyncio.sleep(0)

            partial_func = asyncio.coroutine(functools.partial(func, 1))
            task = self.loop.create_task(partial_func(2))

            # make warnings quiet
            task._log_destroy_pending = False
            self.addCleanup(task._coro.close)

        coro_repr = repr(task._coro)
        expected = (
            r'<CoroWrapper \w+.test_task_repr_partial_corowrapper'
            r'\.<locals>\.func\(1\)\(\) running, '
        )
        self.assertRegex(coro_repr, expected)

    def test_task_basics(self):
        @asyncio.coroutine
        def outer():
            a = yield from inner1()
            b = yield from inner2()
            return a+b

        @asyncio.coroutine
        def inner1():
            return 42

        @asyncio.coroutine
        def inner2():
            return 1000

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

    def test_cancel(self):

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

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def task():
            yield from asyncio.sleep(10.0, loop=loop)
            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_yield(self):
        @asyncio.coroutine
        def task():
            yield
            yield
            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)

        @asyncio.coroutine
        def task():
            yield from 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)

        @asyncio.coroutine
        def task():
            yield from 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)

        @asyncio.coroutine
        def task():
            yield from fut1
            try:
                yield from 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)

        @asyncio.coroutine
        def task():
            yield from fut1
            try:
                yield from fut2
            except asyncio.CancelledError:
                pass
            res = yield from 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)

        @asyncio.coroutine
        def task():
            t.cancel()
            self.assertTrue(t._must_cancel)  # White-box test.
            # The sleep should be cancelled immediately.
            yield from asyncio.sleep(100, loop=loop)
            return 12

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

    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
        waiters = []

        @asyncio.coroutine
        def task():
            nonlocal x
            while x < 10:
                waiters.append(asyncio.sleep(0.1, loop=loop))
                yield from waiters[-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())

        # close generators
        for w in waiters:
            w.close()
        t.cancel()
        self.assertRaises(asyncio.CancelledError, loop.run_until_complete, t)

    def test_wait_for(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.2, when)
            when = yield 0
            self.assertAlmostEqual(0.1, when)
            when = yield 0.1

        loop = self.new_test_loop(gen)

        foo_running = None

        @asyncio.coroutine
        def foo():
            nonlocal foo_running
            foo_running = True
            try:
                yield from asyncio.sleep(0.2, loop=loop)
            finally:
                foo_running = False
            return 'done'

        fut = self.new_task(loop, foo())

        with self.assertRaises(asyncio.TimeoutError):
            loop.run_until_complete(asyncio.wait_for(fut, 0.1, loop=loop))
        self.assertTrue(fut.done())
        # it should have been cancelled due to the timeout
        self.assertTrue(fut.cancelled())
        self.assertAlmostEqual(0.1, loop.time())
        self.assertEqual(foo_running, False)

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

        @asyncio.coroutine
        def coro():
            return 'done'

        res = loop.run_until_complete(asyncio.wait_for(coro(),
                                                       timeout=None,
                                                       loop=loop))
        self.assertEqual(res, 'done')

    def test_wait_for_with_global_loop(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.2, when)
            when = yield 0
            self.assertAlmostEqual(0.01, when)
            yield 0.01

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def foo():
            yield from asyncio.sleep(0.2, loop=loop)
            return 'done'

        asyncio.set_event_loop(loop)
        try:
            fut = self.new_task(loop, foo())
            with self.assertRaises(asyncio.TimeoutError):
                loop.run_until_complete(asyncio.wait_for(fut, 0.01))
        finally:
            asyncio.set_event_loop(None)

        self.assertAlmostEqual(0.01, loop.time())
        self.assertTrue(fut.done())
        self.assertTrue(fut.cancelled())

    def test_wait_for_race_condition(self):

        def gen():
            yield 0.1
            yield 0.1
            yield 0.1

        loop = self.new_test_loop(gen)

        fut = self.new_future(loop)
        task = asyncio.wait_for(fut, timeout=0.2, loop=loop)
        loop.call_later(0.1, fut.set_result, "ok")
        res = loop.run_until_complete(task)
        self.assertEqual(res, "ok")

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

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a], loop=loop)
            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_with_global_loop(self):

        def gen():
            when = yield
            self.assertAlmostEqual(0.01, when)
            when = yield 0
            self.assertAlmostEqual(0.015, when)
            yield 0.015

        loop = self.new_test_loop(gen)

        a = self.new_task(loop, asyncio.sleep(0.01, loop=loop))
        b = self.new_task(loop, asyncio.sleep(0.015, loop=loop))

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a])
            self.assertEqual(done, set([a, b]))
            self.assertEqual(pending, set())
            return 42

        asyncio.set_event_loop(loop)
        res = loop.run_until_complete(
            self.new_task(loop, foo()))

        self.assertEqual(res, 42)

    def test_wait_duplicate_coroutines(self):
        @asyncio.coroutine
        def coro(s):
            return s
        c = coro('test')

        task =self.new_task(
            self.loop,
            asyncio.wait([c, c, coro('spam')], loop=self.loop))

        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(), loop=self.loop))

        # -1 is an invalid return_when value
        sleep_coro = asyncio.sleep(10.0, loop=self.loop)
        wait_coro = asyncio.wait([sleep_coro], return_when=-1, loop=self.loop)
        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, loop=loop))
        b = self.new_task(loop, asyncio.sleep(0.1, loop=loop))
        task = self.new_task(
            loop,
            asyncio.wait([b, a], return_when=asyncio.FIRST_COMPLETED,
                         loop=loop))

        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], loop=loop))

    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

        @asyncio.coroutine
        def coro1():
            yield

        @asyncio.coroutine
        def coro2():
            yield
            yield

        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,
                         loop=self.loop))

        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, loop=loop))

        @asyncio.coroutine
        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,
                         loop=loop))

        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], loop=loop))

    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, loop=loop))

        @asyncio.coroutine
        def exc():
            yield from asyncio.sleep(0.01, loop=loop)
            raise ZeroDivisionError('err')

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

        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], loop=loop))

    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, loop=loop))

        @asyncio.coroutine
        def sleeper():
            yield from asyncio.sleep(0.15, loop=loop)
            raise ZeroDivisionError('really')

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

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a], loop=loop)
            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, loop=loop))
        b = self.new_task(loop, asyncio.sleep(0.15, loop=loop))

        @asyncio.coroutine
        def foo():
            done, pending = yield from asyncio.wait([b, a], timeout=0.11,
                                                    loop=loop)
            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], loop=loop))

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

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

        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], loop=loop))

    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

        @asyncio.coroutine
        def sleeper(dt, x):
            nonlocal time_shifted
            yield from asyncio.sleep(dt, loop=loop)
            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')

        @asyncio.coroutine
        def foo():
            values = []
            for f in asyncio.as_completed([b, c, a], loop=loop):
                values.append((yield from 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')

        # 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())

    def test_as_completed_with_timeout(self):

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

        loop = self.new_test_loop(gen)

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

        @asyncio.coroutine
        def foo():
            values = []
            for f in asyncio.as_completed([a, b], timeout=0.12, loop=loop):
                if values:
                    loop.advance_time(0.02)
                try:
                    v = yield from 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], loop=loop))

    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', loop=loop)

        @asyncio.coroutine
        def foo():
            for f in asyncio.as_completed([a], timeout=1, loop=loop):
                v = yield from 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', loop=loop)
        b = asyncio.sleep(0.10, 'b', loop=loop)
        fs = {a, b}
        futs = list(asyncio.as_completed(fs, loop=loop))
        self.assertEqual(len(futs), 2)

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

    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

        loop = self.new_test_loop(gen)

        a = asyncio.sleep(0.05, 'a', loop=loop)
        b = asyncio.sleep(0.05, 'b', loop=loop)
        fs = {a, b}
        futs = list(asyncio.as_completed(fs, loop=loop))
        self.assertEqual(len(futs), 2)
        waiter = asyncio.wait(futs, loop=loop)
        done, pending = loop.run_until_complete(waiter)
        self.assertEqual(set(f.result() for f in done), {'a', 'b'})

    def test_as_completed_duplicate_coroutines(self):

        @asyncio.coroutine
        def coro(s):
            return s

        @asyncio.coroutine
        def runner():
            result = []
            c = coro('ham')
            for f in asyncio.as_completed([c, c, coro('spam')],
                                          loop=self.loop):
                result.append((yield from 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_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)

        @asyncio.coroutine
        def sleeper(dt, arg):
            yield from asyncio.sleep(dt/2, loop=loop)
            res = yield from asyncio.sleep(dt/2, arg, loop=loop)
            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', loop=loop))

        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)

        @asyncio.coroutine
        def sleep(dt):
            yield from asyncio.sleep(dt, loop=loop)

        @asyncio.coroutine
        def doit():
            sleeper = self.new_task(loop, sleep(5000))
            loop.call_later(0.1, sleeper.cancel)
            try:
                yield from 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)

        @asyncio.coroutine
        def coro():
            yield from 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_step_in_completed_task(self):
        @asyncio.coroutine
        def notmuch():
            return 'ko'

        gen = notmuch()
        task = self.new_task(self.loop, gen)
        task.set_result('ok')

        self.assertRaises(AssertionError, task._step)
        gen.close()

    def test_step_result(self):
        @asyncio.coroutine
        def notmuch():
            yield None
            yield 1
            return 'ko'

        self.assertRaises(
            RuntimeError, self.loop.run_until_complete, notmuch())

    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, fn):
                self.cb_added = True
                super().add_done_callback(fn)

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

        @asyncio.coroutine
        def wait_for_future():
            nonlocal result
            result = yield from 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_step_with_baseexception(self):
        @asyncio.coroutine
        def notmutch():
            raise BaseException()

        task = self.new_task(self.loop, notmutch())
        self.assertRaises(BaseException, task._step)

        self.assertTrue(task.done())
        self.assertIsInstance(task.exception(), BaseException)

    def test_baseexception_during_cancel(self):

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

        loop = self.new_test_loop(gen)

        @asyncio.coroutine
        def sleeper():
            yield from asyncio.sleep(10, loop=loop)

        base_exc = BaseException()

        @asyncio.coroutine
        def notmutch():
            try:
                yield from 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(BaseException, 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))

        @asyncio.coroutine
        def fn2():
            yield
        self.assertTrue(asyncio.iscoroutinefunction(fn2))

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

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

        @asyncio.coroutine
        def wait_for_future():
            yield fut

        task = wait_for_future()
        with self.assertRaises(RuntimeError):
            self.loop.run_until_complete(task)

        self.assertFalse(fut.done())

    def test_yield_vs_yield_from_generator(self):
        @asyncio.coroutine
        def coro():
            yield

        @asyncio.coroutine
        def wait_for_future():
            gen = coro()
            try:
                yield gen
            finally:
                gen.close()

        task = wait_for_future()
        self.assertRaises(
            RuntimeError,
            self.loop.run_until_complete, task)

    def test_coroutine_non_gen_function(self):
        @asyncio.coroutine
        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)

        @asyncio.coroutine
        def func():
            return fut

        @asyncio.coroutine
        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, 'test')
        self.assertIsNone(t2.result())

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

        self.assertIsNone(Task.current_task(loop=self.loop))

        @asyncio.coroutine
        def coro(loop):
            self.assertTrue(Task.current_task(loop=loop) is task)

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

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

        self.assertIsNone(Task.current_task(loop=self.loop))

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

        @asyncio.coroutine
        def coro1(loop):
            self.assertTrue(Task.current_task(loop=loop) is task1)
            yield from fut1
            self.assertTrue(Task.current_task(loop=loop) is task1)
            fut2.set_result(True)

        @asyncio.coroutine
        def coro2(loop):
            self.assertTrue(Task.current_task(loop=loop) is task2)
            fut1.set_result(True)
            yield from fut2
            self.assertTrue(Task.current_task(loop=loop) 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),
                                                  loop=self.loop))
        self.assertIsNone(Task.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)

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

        @asyncio.coroutine
        def outer():
            nonlocal proof
            try:
                yield from 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)

        @asyncio.coroutine
        def inner():
            nonlocal proof
            yield from waiter
            proof += 1

        @asyncio.coroutine
        def outer():
            nonlocal proof
            d, p = yield from asyncio.wait([inner()], loop=self.loop)
            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(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_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)

        @asyncio.coroutine
        def inner():
            nonlocal proof
            yield from waiter
            proof += 1

        @asyncio.coroutine
        def outer():
            nonlocal proof
            yield from asyncio.shield(inner(), loop=self.loop)
            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, loop=self.loop)
        outer = asyncio.shield(parent, loop=self.loop)
        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, loop=self.loop)
        inner2 = asyncio.shield(child2, loop=self.loop)
        parent = asyncio.gather(inner1, inner2, loop=self.loop)
        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_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, loop=self.loop))
        coro = coroutine_function()
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.as_completed(coro, loop=self.loop))
        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, loop=self.loop))
        coro = coroutine_function()
        self.assertRaises(TypeError, self.loop.run_until_complete,
            asyncio.wait(coro, loop=self.loop))
        coro.close()

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

    def test_corowrapper_mocks_generator(self):

        def check():
            # A function that asserts various things.
            # Called twice, with different debug flag values.

            @asyncio.coroutine
            def coro():
                # The actual coroutine.
                self.assertTrue(gen.gi_running)
                yield from fut

            # A completed Future used to run the coroutine.
            fut = self.new_future(self.loop)
            fut.set_result(None)

            # Call the coroutine.
            gen = coro()

            # Check some properties.
            self.assertTrue(asyncio.iscoroutine(gen))
            self.assertIsInstance(gen.gi_frame, types.FrameType)
            self.assertFalse(gen.gi_running)
            self.assertIsInstance(gen.gi_code, types.CodeType)

            # Run it.
            self.loop.run_until_complete(gen)

            # The frame should have changed.
            self.assertIsNone(gen.gi_frame)

        # Test with debug flag cleared.
        with set_coroutine_debug(False):
            check()

        # Test with debug flag set.
        with set_coroutine_debug(True):
            check()

    def test_yield_from_corowrapper(self):
        with set_coroutine_debug(True):
            @asyncio.coroutine
            def t1():
                return (yield from t2())

            @asyncio.coroutine
            def t2():
                f = self.new_future(self.loop)
                self.new_task(self.loop, t3(f))
                return (yield from f)

            @asyncio.coroutine
            def t3(f):
                f.set_result((1, 2, 3))

            task = self.new_task(self.loop, t1())
            val = self.loop.run_until_complete(task)
            self.assertEqual(val, (1, 2, 3))

    def test_yield_from_corowrapper_send(self):
        def foo():
            a = yield
            return a

        def call(arg):
            cw = asyncio.coroutines.CoroWrapper(foo())
            cw.send(None)
            try:
                cw.send(arg)
            except StopIteration as ex:
                return ex.args[0]
            else:
                raise AssertionError('StopIteration was expected')

        self.assertEqual(call((1, 2)), (1, 2))
        self.assertEqual(call('spam'), 'spam')

    def test_corowrapper_weakref(self):
        wd = weakref.WeakValueDictionary()
        def foo(): yield from []
        cw = asyncio.coroutines.CoroWrapper(foo())
        wd['cw'] = cw  # Would fail without __weakref__ slot.
        cw.gen = None  # Suppress warning from __del__.

    def test_corowrapper_throw(self):
        # Issue 429: CoroWrapper.throw must be compatible with gen.throw
        def foo():
            value = None
            while True:
                try:
                    value = yield value
                except Exception as e:
                    value = e

        exception = Exception("foo")
        cw = asyncio.coroutines.CoroWrapper(foo())
        cw.send(None)
        self.assertIs(exception, cw.throw(exception))

        cw = asyncio.coroutines.CoroWrapper(foo())
        cw.send(None)
        self.assertIs(exception, cw.throw(Exception, exception))

        cw = asyncio.coroutines.CoroWrapper(foo())
        cw.send(None)
        exception = cw.throw(Exception, "foo")
        self.assertIsInstance(exception, Exception)
        self.assertEqual(exception.args, ("foo", ))

        cw = asyncio.coroutines.CoroWrapper(foo())
        cw.send(None)
        exception = cw.throw(Exception, "foo", None)
        self.assertIsInstance(exception, Exception)
        self.assertEqual(exception.args, ("foo", ))

    @unittest.skipUnless(PY34,
                         'need python 3.4 or later')
    def test_log_destroyed_pending_task(self):
        Task = self.__class__.Task

        @asyncio.coroutine
        def kill_me(loop):
            future = self.new_future(loop)
            yield from 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(Task.all_tasks(loop=self.loop), {task})

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

        # remove the future used in kill_me(), and references to the task
        del coro.gi_frame.f_locals['future']
        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(Task.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.coroutines.logger')
    def test_coroutine_never_yielded(self, m_log):
        with set_coroutine_debug(True):
            @asyncio.coroutine
            def coro_noop():
                pass

        tb_filename = __file__
        tb_lineno = sys._getframe().f_lineno + 2
        # create a coroutine object but don't use it
        coro_noop()
        support.gc_collect()

        self.assertTrue(m_log.error.called)
        message = m_log.error.call_args[0][0]
        func_filename, func_lineno = test_utils.get_function_source(coro_noop)

        regex = (r'^<CoroWrapper %s\(?\)? .* at %s:%s, .*> '
                    r'was never yielded from\n'
                 r'Coroutine object created at \(most recent call last\):\n'
                 r'.*\n'
                 r'  File "%s", line %s, in test_coroutine_never_yielded\n'
                 r'    coro_noop\(\)$'
                 % (re.escape(coro_noop.__qualname__),
                    re.escape(func_filename), func_lineno,
                    re.escape(tb_filename), tb_lineno))

        self.assertRegex(message, re.compile(regex, re.DOTALL))

    def test_return_coroutine_from_coroutine(self):
        """Return of @asyncio.coroutine()-wrapped function generator object
        from @asyncio.coroutine()-wrapped function should have same effect as
        returning generator object or Future."""
        def check():
            @asyncio.coroutine
            def outer_coro():
                @asyncio.coroutine
                def inner_coro():
                    return 1

                return inner_coro()

            result = self.loop.run_until_complete(outer_coro())
            self.assertEqual(result, 1)

        # Test with debug flag cleared.
        with set_coroutine_debug(False):
            check()

        # Test with debug flag set.
        with set_coroutine_debug(True):
            check()

    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_wait_for(self, timeout):
        loop = asyncio.new_event_loop()
        self.addCleanup(loop.close)

        @asyncio.coroutine
        def blocking_coroutine():
            fut = self.new_future(loop)
            # Block: fut result is never set
            yield from fut

        task = loop.create_task(blocking_coroutine())

        wait = loop.create_task(asyncio.wait_for(task, timeout, loop=loop))
        loop.call_soon(wait.cancel)

        self.assertRaises(asyncio.CancelledError,
                          loop.run_until_complete, wait)

        # Python issue #23219: cancelling the wait must also cancel the task
        self.assertTrue(task.cancelled())

    def test_cancel_blocking_wait_for(self):
        self._test_cancel_wait_for(None)

    def test_cancel_wait_for(self):
        self._test_cancel_wait_for(60.0)

    def test_cancel_gather(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)
        # 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(), loop=loop)
        gather_task = asyncio.ensure_future(gather_future, loop=loop)

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

        @asyncio.coroutine
        def foo():
            1 / 0

        @asyncio.coroutine
        def main():
            task = self.new_task(self.loop, foo())
            yield  # 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):
            raise ValueError
        self.loop.call_soon = call_soon

        @asyncio.coroutine
        def coro():
            pass

        self.assertFalse(m_log.error.called)

        with self.assertRaises(ValueError):
            self.new_task(self.loop, coro())

        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(self.Task.all_tasks(self.loop), set())


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 _schedule_callbacks(self):
            self.calls['_schedule_callbacks'] += 1
            return super()._schedule_callbacks()

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

    class Task(CommonFuture, BaseTask):
        def _step(self, *args):
            self.calls['_step'] += 1
            return super()._step(*args)

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

    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),
            {'_step': 2, '_wakeup': 1, 'add_done_callback': 1,
             '_schedule_callbacks': 1})

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

    # 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


@unittest.skipUnless(hasattr(futures, '_CFuture'),
                     'requires the C _asyncio module')
class CTask_CFuture_Tests(BaseTaskTests, test_utils.TestCase):
    Task = getattr(tasks, '_CTask', None)
    Future = getattr(futures, '_CFuture', None)


@unittest.skipUnless(hasattr(futures, '_CFuture'),
                     '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(futures, '_CFuture'),
                     '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, 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


class GenericTaskTests(test_utils.TestCase):

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

    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), but _asyncio somehow didn't.
        try:
            import _functools
        except ImportError:
            pass
        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 = [asyncio.Future(loop=self.one_loop) for i in range(3)]
        fut = asyncio.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 = [asyncio.Future(loop=self.one_loop) for i in range(5)]
        fut = asyncio.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 = [asyncio.Future(loop=self.one_loop) for i in range(4)]
        fut = asyncio.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):
        aio_path = os.path.dirname(os.path.dirname(asyncio.__file__))

        code = '\n'.join((
            'import asyncio.coroutines',
            'print(asyncio.coroutines._DEBUG)'))

        # 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,
                                               PYTHONPATH=aio_path)
        self.assertEqual(stdout.rstrip(), b'False')

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

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

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


class FutureGatherTests(GatherTestsBase, test_utils.TestCase):

    def wrap_futures(self, *futures):
        return futures

    def _check_empty_sequence(self, seq_or_iter):
        asyncio.set_event_loop(self.one_loop)
        self.addCleanup(asyncio.set_event_loop, None)
        fut = asyncio.gather(*seq_or_iter)
        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(), [])
        fut = asyncio.gather(*seq_or_iter, loop=self.other_loop)
        self.assertIs(fut._loop, self.other_loop)

    def test_constructor_empty_sequence(self):
        self._check_empty_sequence([])
        self._check_empty_sequence(())
        self._check_empty_sequence(set())
        self._check_empty_sequence(iter(""))

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

    def test_constructor_homogenous_futures(self):
        children = [asyncio.Future(loop=self.other_loop) 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, loop=self.other_loop)
        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 = [asyncio.Future(loop=self.one_loop) 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 = [asyncio.Future(loop=self.one_loop)
                            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 setUp(self):
        super().setUp()
        asyncio.set_event_loop(self.one_loop)

    def wrap_futures(self, *futures):
        coros = []
        for fut in futures:
            @asyncio.coroutine
            def coro(fut=fut):
                return (yield from fut)
            coros.append(coro())
        return coros

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

        self.set_event_loop(self.other_loop, cleanup=False)
        gen3 = coro()
        gen4 = coro()
        fut2 = asyncio.gather(gen3, gen4, loop=self.other_loop)
        self.assertIs(fut2._loop, self.other_loop)
        self.other_loop.run_until_complete(fut2)

    def test_duplicate_coroutines(self):
        @asyncio.coroutine
        def coro(s):
            return s
        c = coro('abc')
        fut = asyncio.gather(c, c, coro('def'), c, loop=self.one_loop)
        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 = asyncio.Future(loop=self.one_loop)

        @asyncio.coroutine
        def inner():
            nonlocal proof
            yield from waiter
            proof += 1

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

        @asyncio.coroutine
        def outer():
            nonlocal proof, gatherer
            gatherer = asyncio.gather(child1, child2, loop=self.one_loop)
            yield from 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."

        @asyncio.coroutine
        def inner(f):
            yield from f
            raise RuntimeError('should not be ignored')

        a = asyncio.Future(loop=self.one_loop)
        b = asyncio.Future(loop=self.one_loop)

        @asyncio.coroutine
        def outer():
            yield from asyncio.gather(inner(a), inner(b), loop=self.one_loop)

        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)


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

    @asyncio.coroutine
    def add(self, a, b, fail=False, cancel=False):
        """Wait 0.05 second and return a + b."""
        yield from asyncio.sleep(0.05, loop=self.loop)
        if fail:
            raise RuntimeError("Fail!")
        if cancel:
            asyncio.tasks.Task.current_task(self.loop).cancel()
            yield
        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, so that
            # CoroWrapper.__del__ won't do anything when asyncio tests run
            # in debug mode.
            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.Task.all_tasks(self.loop):
            self.assertTrue(task.done())

    def test_run_coroutine_threadsafe_task_cancelled(self):
        """Test coroutine submission from a tread 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 tread to an event loop
        when the task factory raise an exception."""
        # Schedule the target
        future = self.loop.run_in_executor(
            None, lambda: self.target(advance_coro=True))
        # Set corrupted task factory
        self.loop.set_task_factory(lambda loop, coro: wrong_name)
        # Set exception handler
        callback = test_utils.MockCallback()
        self.loop.set_exception_handler(callback)
        # Run event loop
        with self.assertRaises(NameError) as exc_context:
            self.loop.run_until_complete(future)
        # Check exceptions
        self.assertIn('wrong_name', exc_context.exception.args[0])
        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()
        asyncio.set_event_loop(None)

    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

        @asyncio.coroutine
        def coro():
            self.loop.call_soon(inc_result, 1)
            self.assertEqual(result, 0)
            num = yield from asyncio.sleep(0, loop=self.loop, 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)


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