Mockin' asyncio coroutine

import asyncio
import unittest
import unittest.mock


class MyClass:

    @asyncio.coroutine
    def coro1(self):
        yield from self.coro2()

    @asyncio.coroutine
    def coro2(self):
        return True


class MockTestCase(unittest.TestCase):

    def test_call_coro2(self):
        loop = asyncio.get_event_loop()
        m = MyClass()
        mm = unittest.mock.MagicMock()
        mm.iter.return_value = 'iterable'
        m.coro2 = unittest.mock.Mock(return_value=mm)
        coro = m.coro1()
        result = loop.run_until_complete(coro)
        self.assertEqual(1, mm.__iter__.call_count)

When I run this, result is None; I'd expect it to be 'iterable' since that's what's being assigned for the return_value. Is there some way to actually set the return value for the mocked method?