pytest-asyncio 0.5.0

Pytest support for asyncio.

pytest-asyncio is an Apache2 licensed library, written in Python, for testing asyncio code with pytest.

asyncio code is usually written in the form of coroutines, which makes it slightly more difficult to test using normal testing tools. pytest-asyncio provides useful fixtures and markers to make testing easier.

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

or, if you’re using the pre-Python 3.5 syntax:

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

pytest-asyncio has been strongly influenced by pytest-tornado.

Features

• fixtures for creating and injecting versions of the asyncio event loop

• fixtures for injecting unused tcp ports

• pytest markers for treating tests as asyncio coroutines

• easy testing with non-default event loops

Installation

To install pytest-asyncio, simply:

$ pip install pytest-asyncio

This is enough for pytest to pick up pytest-asyncio.

Fixtures

event_loop

Creates and injects a new instance of the default asyncio event loop. By default, the loop will be closed at the end of the test (i.e. the default fixture scope is function).

Note that just using the event_loop fixture won’t make your test function a coroutine. You’ll need to interact with the event loop directly, using methods like event_loop.run_until_complete. See the pytest.mark.asyncio marker for treating test functions like coroutines.

def test_http_client(event_loop):
    url = 'http://httpbin.org/get'
    resp = event_loop.run_until_complete(http_client(url))
    assert b'HTTP/1.1 200 OK' in resp

This fixture can be easily overridden in any of the standard pytest locations (e.g. directly in the test file, or in conftest.py) to use a non-default event loop. This will take effect even if you’re using the pytest.mark.asyncio marker and not the event_loop fixture directly.

@pytest.yield_fixture()
def event_loop():
    loop = MyCustomLoop()
    yield loop
    loop.close()

A special pytest hook will ensure the produced loop is either set as the default global loop, or a special, error-throwing event loop policy is installed as the default policy (depending on the forbid_global_loop parameter). Fixtures depending on the event_loop fixture can expect the policy to be properly modified when they run.

event_loop_process_pool

The event_loop_process_pool fixture is almost identical to the event_loop fixture, except the created event loop will have a concurrent.futures.ProcessPoolExecutor set as the default executor.

unused_tcp_port

Finds and yields a single unused TCP port on the localhost interface. Useful for binding temporary test servers.

unused_tcp_port_factory

A callable which returns a different unused TCP port each invocation. Useful when several unused TCP ports are required in a test.

def a_test(unused_tcp_port_factory):
    port1, port2 = unused_tcp_port_factory(), unused_tcp_port_factory()
    ...

Markers

pytest.mark.asyncio(forbid_global_loop=False)

Mark your test coroutine with this marker and pytest will execute it as an asyncio task using the event loop provided by the event_loop fixture. See the introductory section for an example.

The event loop used can be overriden by overriding the event_loop fixture (see above).

If forbid_global_loop is true, asyncio.get_event_loop() will result in exceptions, ensuring your tests are always passing the event loop explicitly.

pytest.mark.asyncio_process_pool(forbid_global_loop=False)

The asyncio_process_pool marker is almost identical to the asyncio marker, except the event loop used will have a concurrent.futures.ProcessPoolExecutor set as the default executor.

Changelog

0.5.0 (2016-09-07)

• Introduced a changelog. #31

• The event_loop fixture is again responsible for closing itself. This makes the fixture slightly harder to correctly override, but enables other fixtures to depend on it correctly. #30

• Deal with the event loop policy by wrapping a special pytest hook, pytest_fixture_setup. This allows setting the policy before fixtures dependent on the event_loop fixture run, thus allowing them to take advantage of the forbid_global_loop parameter. As a consequence of this, we now depend on pytest 3.0. #29

0.4.1 (2016-06-01)

• Fix a bug preventing the propagation of exceptions from the plugin. #25

0.4.0 (2016-05-30)

• Make event_loop fixtures simpler to override by closing them in the plugin, instead of directly in the fixture. #21

• Introduce the forbid_global_loop parameter. #21

0.3.0 (2015-12-19)

• Support for Python 3.5 async/await syntax. #17

0.2.0 (2015-08-01)

• unused_tcp_port_factory fixture. #10

0.1.1 (2015-04-23)

Initial release.

Contributing

Contributions are very welcome. Tests can be run with tox, please ensure the coverage at least stays the same before you submit a pull request.