Pytest setup that runs first during fixture setup stage

__init__.py

__all__ = ()

conftest.py

import logging
from typing import Set

import pytest


logger = logging.getLogger(__name__)


def pytest_configure(config: pytest.Config) -> None:
    config.addinivalue_line(
        "markers",
        "require_features(FEAT, ...): specify required host features",
    )


@pytest.fixture(scope="session")
def host(pytestconfig: pytest.Config) -> str:
    if address := pytestconfig.getoption("host_address", None):
        logger.info("Using host address %s", address)
        return address
    else:
        logger.info("Using localhost")
        return "localhost"


@pytest.fixture(scope="session", autouse=True)
def _skip_marked_tests_as_applicable(request: pytest.FixtureRequest, host: str) -> None:
    session = request.node
    host_features = _detect_host_features(host)

    for item in session.items:
        if mark := item.get_closest_marker("require_features"):
            required_features = set(mark.args)
        else:
            required_features = set()

        missing_features = required_features - host_features
        if missing_features:
            item.add_marker(
                pytest.mark.skip(
                    f"Host missing features: " + ",".join(sorted(missing_features))
                )
            )


def _detect_host_features(host: str) -> Set[str]:
    # Run commands on the host over SSH to determine what features it provides.
    ...
    return {"bar", "baz"}

output.txt

$PYTEST_PLUGINS=tests.plugin pytest tests/ --log-cli-level info --setup-vm
=============================================================== test session starts ===============================================================
platform linux -- Python 3.9.12, pytest-7.2.0, pluggy-1.0.0
rootdir: pytest-playground, configfile: pytest.ini
collected 3 items

tests/test_1.py::test_A
----------------------------------------------------------------- live log setup ------------------------------------------------------------------
INFO     tests.plugin:plugin.py:38 Booting VM...
INFO     tests.conftest:conftest.py:22 Using VM host 10.0.0.123
------------------------------------------------------------------ live log call ------------------------------------------------------------------
INFO     tests.test_1:test_1.py:10 Running test A
PASSED                                                                                                                                      [ 33%]
tests/test_1.py::test_B SKIPPED (Host missing features: foo)                                                                    [ 66%]
tests/test_1.py::test_C
------------------------------------------------------------------ live log call ------------------------------------------------------------------
INFO     tests.test_1:test_1.py:20 Running test C
PASSED                                                                                                                                      [100%]
---------------------------------------------------------------- live log teardown ----------------------------------------------------------------
INFO     tests.plugin:plugin.py:43 Tearing down the VM...


========================================================== 2 passed, 1 skipped in 0.03s ===========================================================

plugin.py

import logging
from typing import List

import pytest


logger = logging.getLogger(__name__)


def pytest_addoption(parser: pytest.Parser) -> None:
    group = parser.getgroup("vm_opts", "VM plugin opts")
    group.addoption(
        "--setup-vm",
        action="store_true",
        help="Enable setting up a VM",
    )


def pytest_configure(config: pytest.Config) -> None:
    if config.option.setup_vm:
        config.option.host_address = "10.0.0.123"


def pytest_collection_modifyitems(
    config: pytest.Config, items: List[pytest.Item]
) -> None:
    # Force setup fixture to run first.
    # Added as a dependency for all tests (effectively like autouse).
    if config.option.setup_vm:
        for item in items:
            item.fixturenames.insert(0, "vm_setup")


@pytest.fixture(scope="session")
def vm_setup() -> None:
    _boot_vm()
    yield
    _teardown_vm()


def _boot_vm():
    logger.info("Booting VM...")
    ...


def _teardown_vm():
    logger.info("Tearing down the VM...")
    ...

test_1.py

import logging

import pytest


logger = logging.getLogger(__name__)


def test_A(host):
    logger.info("Running test A")


@pytest.mark.require_features("foo")
def test_B(host):
    logger.info("Running test B")


@pytest.mark.require_features("bar")
def test_C(host):
    logger.info("Running test C")