使用asyncio事件循环运行tornado.testing.AsyncTestCase

Question

I have an asyncio based class which I want to unit test. Using tornado.testing.AsyncTestCase this works quite well and easily. However, one specific method of my class uses asyncio.ensure_future to schedule execution of another method. This never finishes in the AsyncTestCase , because the default test runner uses the tornado KQueueIOLoop event loop, not an asyncio event loop.

class TestSubject:
    def foo(self):
        asyncio.ensure_future(self.bar())

    async def bar(self):
        pass

class TestSubjectTest(AsyncTestCase):
    def test_foo(self):
        t = TestSubject()
        # here be somewhat involved setup with MagicMock and self.stop
        t.foo()
        self.wait()

$ python -m tornado.testing baz.testsubject_test
...
[E 160627 17:48:22 testing:731] FAIL
[E 160627 17:48:22 base_events:1090] Task was destroyed but it is pending!
    task: <Task pending coro=<TestSubject.bar() running at ...>>
.../asyncio/base_events.py:362: RuntimeWarning: coroutine 'TestSubject.bar' was never awaited

How can I use a different event loop to run the tests on to ensure my task will actually be executed? Alternatively, how can I make my implementation event loop-independent and cross-compatible?

Answer 1

Turns out to be simple enough...

class TestSubjectTest(AsyncTestCase):
    def get_new_ioloop(self):  # override this method
        return tornado.platform.asyncio.AsyncIOMainLoop()

I was trying this before, but directly returned asyncio.get_event_loop() , which didn't work. Returning Tornado's asyncio loop wrapper does the trick.