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.
- 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
To install pytest-asyncio, simply:
$ pip install pytest-asyncio
This is enough for pytest to pick up pytest-asyncio.
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.
Simply using this fixture will not set the generated event loop as the
default asyncio event loop, or change the asyncio event loop policy in any way.
Use pytest.mark.asyncio
for this purpose.
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()
If the pytest.mark.asyncio
marker is applied, a 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.
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.
Finds and yields a single unused TCP port on the localhost interface. Useful for binding temporary test servers.
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()
...
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.
In order to make your test code a little more concise, the pytest pytestmark
feature can be used to mark entire modules or classes with this marker.
Only test coroutines will be affected (by default, coroutines prefixed by
test_
), so, for example, fixtures are safe to define.
import asyncio
import pytest
# All test coroutines will be treated as marked.
pytestmark = pytest.mark.asyncio(forbid_global_loop=True)
async def test_example(event_loop):
"""No marker!"""
await asyncio.sleep(0, loop=event_loop)
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.
pytestmark
now works on both module and class level.- Using
forbid_global_loop
now allows tests to useasyncio
subprocesses. #36
- 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 theevent_loop
fixture run, thus allowing them to take advantage of theforbid_global_loop
parameter. As a consequence of this, we now depend on pytest 3.0. #29
- Fix a bug preventing the propagation of exceptions from the plugin. #25
- 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
- Support for Python 3.5
async
/await
syntax. #17
unused_tcp_port_factory
fixture. #10
Initial release.
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.