How to mock asyncio coroutines?

Springing off of Andrew Svetlov's answer, I just wanted to share this helper function:

def get_mock_coro(return_value):
    @asyncio.coroutine
    def mock_coro(*args, **kwargs):
        return return_value

    return Mock(wraps=mock_coro)

This lets you use the standard assert_called_with, call_count and other methods and attributes a regular unittest.Mock gives you.

You can use this with code in the question like:

class ImGoingToBeMocked:
    @asyncio.coroutine
    def yeah_im_not_going_to_run(self):
        yield from asyncio.sleep(1)
        return "sup"

class ImBeingTested:
    def __init__(self, hidude):
        self.hidude = hidude

    @asyncio.coroutine
    def i_call_other_coroutines(self):
        return (yield from self.hidude.yeah_im_not_going_to_run())

class TestImBeingTested(unittest.TestCase):

    def test_i_call_other_coroutines(self):
        mocked = Mock(ImGoingToBeMocked)
        mocked.yeah_im_not_going_to_run = get_mock_coro()
        ibt = ImBeingTested(mocked)

        ret = asyncio.get_event_loop().run_until_complete(ibt.i_call_other_coroutines())
        self.assertEqual(mocked.yeah_im_not_going_to_run.call_count, 1)

Since mock library doesn't support coroutines I create mocked coroutines manually and assign those to mock object. A bit more verbose but it works.

Your example may look like this:

import asyncio
import unittest
from unittest.mock import Mock


class ImGoingToBeMocked:
    @asyncio.coroutine
    def yeah_im_not_going_to_run(self):
        yield from asyncio.sleep(1)
        return "sup"


class ImBeingTested:
    def __init__(self, hidude):
        self.hidude = hidude

    @asyncio.coroutine
    def i_call_other_coroutines(self):
        return (yield from self.hidude.yeah_im_not_going_to_run())


class TestImBeingTested(unittest.TestCase):

    def test_i_call_other_coroutines(self):
        mocked = Mock(ImGoingToBeMocked)
        ibt = ImBeingTested(mocked)

        @asyncio.coroutine
        def mock_coro():
            return "sup"
        mocked.yeah_im_not_going_to_run = mock_coro

        ret = asyncio.get_event_loop().run_until_complete(
            ibt.i_call_other_coroutines())
        self.assertEqual("sup", ret)


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

I am writting a wrapper to unittest which aims at cutting the boilerplate when writting tests for asyncio.

The code lives here: https://github.com/Martiusweb/asynctest

You can mock a coroutine with asynctest.CoroutineMock:

>>> mock = CoroutineMock(return_value='a result')
>>> asyncio.iscoroutinefunction(mock)
True
>>> asyncio.iscoroutine(mock())
True
>>> asyncio.run_until_complete(mock())
'a result'

It also works with the side_effect attribute, and an asynctest.Mock with a spec can return CoroutineMock:

>>> asyncio.iscoroutinefunction(Foo().coroutine)
True
>>> asyncio.iscoroutinefunction(Foo().function)
False
>>> asynctest.Mock(spec=Foo()).coroutine
<class 'asynctest.mock.CoroutineMock'>
>>> asynctest.Mock(spec=Foo()).function
<class 'asynctest.mock.Mock'>

All the features of unittest.Mock are expected to work correctly (patch(), etc).