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fixtures.rst

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Fixtures

event_loop

Creates a new asyncio event loop based on the current event loop policy. The new loop is available as the return value of this fixture or via asyncio.get_running_loop. The event loop is closed when the fixture scope ends. The fixture scope defaults to function scope.

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

Note that, when using the event_loop fixture, you need to interact with the event loop using methods like event_loop.run_until_complete. If you want to await code inside your test function, you need to write a coroutine and use it as a test function. The asyncio marker is used to mark coroutines that should be treated as test functions.

The event_loop fixture can be overridden in any of the standard pytest locations, e.g. directly in the test file, or in conftest.py. This allows redefining the fixture scope, for example:

@pytest.fixture(scope="module")
def event_loop():
    policy = asyncio.get_event_loop_policy()
    loop = policy.new_event_loop()
    yield loop
    loop.close()

When defining multiple event_loop fixtures, you should ensure that their scopes don't overlap. Each of the fixtures replace the running event loop, potentially without proper clean up. This will emit a warning and likely lead to errors in your tests suite. You can manually check for overlapping event_loop fixtures by running pytest with the --setup-show option.

If you need to change the type of the event loop, prefer setting a custom event loop policy over redefining the event_loop fixture.

If the pytest.mark.asyncio decorator is applied to a test function, the event_loop fixture will be requested automatically by the test function.

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()
    ...

unused_udp_port and unused_udp_port_factory

Works just like their TCP counterparts but returns unused UDP ports.