How to test Python 3.4 asyncio code?

Question

What\'s the best way to write unit tests for code using the Python 3.4 asyncio library? Assume I want to test a TCP client (SocketConnection):

Answer 1

pytest-asyncio looks promising:

@pytest.mark.asyncio
async def test_some_asyncio_code():
    res = await library.do_something()
    assert b'expected result' == res

Answer 2

You can also use aiounittest that takes similar approach as @Andrew Svetlov, @Marvin Killing answers and wrap it in easy to use AsyncTestCase class:

import asyncio
import aiounittest


async def add(x, y):
    await asyncio.sleep(0.1)
    return x + y

class MyTest(aiounittest.AsyncTestCase):

    async def test_async_add(self):
        ret = await add(5, 6)
        self.assertEqual(ret, 11)

    # or 3.4 way
    @asyncio.coroutine
    def test_sleep(self):
        ret = yield from add(5, 6)
        self.assertEqual(ret, 11)

    # some regular test code
    def test_something(self):
        self.assertTrue(true)

As you can see the async case is handled by AsyncTestCase. It supports also synchronous test. There is a possibility to provide custom event loop, just override AsyncTestCase.get_event_loop.

If you prefer (for some reason) the other TestCase class (eg unittest.TestCase), you might use async_test decorator:

import asyncio
import unittest
from aiounittest import async_test


async def add(x, y):
    await asyncio.sleep(0.1)
    return x + y

class MyTest(unittest.TestCase):

    @async_test
    async def test_async_add(self):
        ret = await add(5, 6)
        self.assertEqual(ret, 11)

Answer 3

Since Python 3.8 unittest comes with the IsolatedAsyncioTestCase function, designed for this purpose.

from unittest import IsolatedAsyncioTestCase

class Test(IsolatedAsyncioTestCase):

    async def test_functionality(self):
        result = await functionality()
        self.assertEqual(expected, result)

Answer 4

I usually define my async tests as coroutines and use a decorator for "syncing" them:

import asyncio
import unittest

def sync(coro):
    def wrapper(*args, **kwargs):
        loop = asyncio.get_event_loop()
        loop.run_until_complete(coro(*args, **kwargs))
    return wrapper

class TestSocketConnection(unittest.TestCase):
    def setUp(self):
        self.mock_server = MockServer("localhost", 1337)
        self.socket_connection = SocketConnection("localhost", 1337)

    @sync
    async def test_sends_handshake_after_connect(self):
        await self.socket_connection.connect()
        self.assertTrue(self.mock_server.received_handshake())