how to write fixtures for asyncio code in pytest

Question

I want to use asyncio together with pytest.

here is what I want to do:

• run a server while my test is running - stop the server when it is finished
• in a perfect world I would implement the server as a fixture (using yield)

I like to write test code like this:

def test_add(svr_fixture):
    await asyncio.sleep(100)
    assert m.add(1, 2) == 3   # I like the readability of this and want to restore it

I tried to write the fixture with pytest-asyncio ( https://pypi.python.org/pypi/pytest-asyncio ) but could not figure out how to do this.

What I came up with it this test (works but it looks clumsy and disguises the intention of the test):

def test_add():
    async def do_it():
        await asyncio.sleep(100)
        return m.add(1, 2)

    loop = asyncio.get_event_loop()
    coro = loop.create_server(server.ServerProtocol, '127.0.0.1', 8023)
    asyncio.async(coro)
    res = loop.run_until_complete(do_it())
    assert res == 3

Any help on how to extract the server code into a fixture like a link to docs or a sample would be much appreciated.

I do not think the complete server code is necessary (but it is here: https://stackoverflow.com/a/48277838/570293 )

Answer 1

Like I pointed out in my question I do not want the async stuff to bloat up my testcases. The only simple working solution I could find so far is to use multiprocessing. I understand that process.terminate() is not the "optimal way" to end the asyncio loop but at least it works reliably.

# -*- coding: utf-8 -*-
import time
from multiprocessing import Process

import pytest
from my_server import server


@pytest.fixture
def fake_server():
    p = Process(target=server.run, args=())
    p.start()

    yield
    p.terminate()


def test_add2(fake_server):
    time.sleep(30)
    assert m.add(1, 2) == 3