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):

import asyncio
import unittest

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

    @asyncio.coroutine
    def test_sends_handshake_after_connect(self):
        yield from self.socket_connection.connect()
        self.assertTrue(self.mock_server.received_handshake())

When running this test case with the default test runner, the test will always succeed as the method executes only up until the first yield from instruction, after which it returns before executing any assertions. This causes tests to always succeed.

Is there a prebuilt test runner that is able to handle asynchronous code like this?

Answer 1

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)