A mark decorator "pytest.mark.boxed" to run a test in forked process.

conftest.py

# -*- coding: utf-8 -*-
import multiprocessing

from _pytest import runner


def pytest_runtest_protocol(item):
    if 'boxed' in item.keywords:
        reports = boxed_run_report(item)
        for rep in reports:
            item.ihook.pytest_runtest_logreport(report=rep)
        return True


def boxed_run_report(item):
    """Seems to be :func:`xdist.plugin.forked_run_report` but it uses
    :mod:`multiprocessing`.
    """
    EXITSTATUS_TESTEXIT = 4
    def run_test(pipe):
        pipe.send(runner.runtestprotocol(item, log=False))
    pipe_in, pipe_out = multiprocessing.Pipe()
    proc = multiprocessing.Process(target=run_test, args=(pipe_in,))
    proc.start()
    proc.join()
    if pipe_out.poll():
        return pipe_out.recv()
    else:
        path, lineno = item._getfslineno()
        call = runner.CallInfo(lambda: 0/0, '???')
        call.excinfo = ('{0}:{1}: running the test CRASHED with '
                        'exit code {2}'.format(path, lineno, proc.exitcode))
        return [runner.pytest_runtest_makereport(item, call)]

test.py

# -*- coding: utf-8 -*-
import os

import pytest


PID = os.getpid()


def test_non_boxing():
    assert PID == os.getpid()


@pytest.mark.boxed
def test_boxing():
    assert PID != os.getpid()
    assert PID == os.getppid()