pytest-xdist 2.4.0

Installation

Install the plugin with:

pip install pytest-xdist

To use psutil for detection of the number of CPUs available, install the psutil extra:

pip install pytest-xdist[psutil]

Speed up test runs by sending tests to multiple CPUs

To send tests to multiple CPUs, use the -n (or --numprocesses) option:

pytest -n NUMCPUS

Pass -n auto to use as many processes as your computer has CPU cores. This can lead to considerable speed ups, especially if your test suite takes a noticeable amount of time.

If a test crashes a worker, pytest-xdist will automatically restart that worker and report the test’s failure. You can use the --max-worker-restart option to limit the number of worker restarts that are allowed, or disable restarting altogether using --max-worker-restart 0.

By default, using --numprocesses will send pending tests to any worker that is available, without any guaranteed order. You can change the test distribution algorithm this with the --dist option. It takes these values:

• --dist no: The default algorithm, distributing one test at a time.

• --dist loadscope: Tests are grouped by module for test functions and by class for test methods. Groups are distributed to available workers as whole units. This guarantees that all tests in a group run in the same process. This can be useful if you have expensive module-level or class-level fixtures. Grouping by class takes priority over grouping by module.

• --dist loadfile: Tests are grouped by their containing file. Groups are distributed to available workers as whole units. This guarantees that all tests in a file run in the same worker.

import json

import pytest
from filelock import FileLock


@pytest.fixture(scope="session")
def session_data(tmp_path_factory, worker_id):
    if worker_id == "master":
        # not executing in with multiple workers, just produce the data and let
        # pytest's fixture caching do its job
        return produce_expensive_data()

    # get the temp directory shared by all workers
    root_tmp_dir = tmp_path_factory.getbasetemp().parent

    fn = root_tmp_dir / "data.json"
    with FileLock(str(fn) + ".lock"):
        if fn.is_file():
            data = json.loads(fn.read_text())
        else:
            data = produce_expensive_data()
            fn.write_text(json.dumps(data))
    return data

Running tests in a Python subprocess

To instantiate a python3.9 subprocess and send tests to it, you may type:

pytest -d --tx popen//python=python3.9

This will start a subprocess which is run with the python3.9 Python interpreter, found in your system binary lookup path.

If you prefix the –tx option value like this:

--tx 3*popen//python=python3.9

then three subprocesses would be created and tests will be load-balanced across these three processes.

Running tests in a boxed subprocess

This functionality has been moved to the pytest-forked plugin, but the --boxed option is still kept for backward compatibility.

Sending tests to remote SSH accounts

Suppose you have a package mypkg which contains some tests that you can successfully run locally. And you have a ssh-reachable machine myhost. Then you can ad-hoc distribute your tests by typing:

pytest -d --tx ssh=myhostpopen --rsyncdir mypkg mypkg

This will synchronize your mypkg package directory to a remote ssh account and then locally collect tests and send them to remote places for execution.

You can specify multiple --rsyncdir directories to be sent to the remote side.

You can specify multiple --rsyncignore glob patterns to be ignored when file are sent to the remote side. There are also internal ignores: .*, *.pyc, *.pyo, *~ Those you cannot override using rsyncignore command-line or ini-file option(s).

Sending tests to remote Socket Servers

Download the single-module socketserver.py Python program and run it like this:

python socketserver.py

It will tell you that it starts listening on the default port. You can now on your home machine specify this new socket host with something like this:

pytest -d --tx socket=192.168.1.102:8888 --rsyncdir mypkg mypkg

Running tests on many platforms at once

The basic command to run tests on multiple platforms is:

pytest --dist=each --tx=spec1 --tx=spec2

If you specify a windows host, an OSX host and a Linux environment this command will send each tests to all platforms - and report back failures from all platforms at once. The specifications strings use the xspec syntax.

Identifying the worker process during a test

New in version 1.15.

If you need to determine the identity of a worker process in a test or fixture, you may use the worker_id fixture to do so:

@pytest.fixture()
def user_account(worker_id):
    """ use a different account in each xdist worker """
    return "account_%s" % worker_id

When xdist is disabled (running with -n0 for example), then worker_id will return "master".

Worker processes also have the following environment variables defined:

• PYTEST_XDIST_WORKER: the name of the worker, e.g., "gw2".

• PYTEST_XDIST_WORKER_COUNT: the total number of workers in this session, e.g., "4" when -n 4 is given in the command-line.

The information about the worker_id in a test is stored in the TestReport as well, under the worker_id attribute.

Since version 2.0, the following functions are also available in the xdist module:

def is_xdist_worker(request_or_session) -> bool:
    """Return `True` if this is an xdist worker, `False` otherwise

    :param request_or_session: the `pytest` `request` or `session` object
    """

def is_xdist_master(request_or_session) -> bool:
    """Return `True` if this is the xdist controller, `False` otherwise

    Note: this method also returns `False` when distribution has not been
    activated at all.

    deprecated alias for is_xdist_controller

    :param request_or_session: the `pytest` `request` or `session` object
    """

 def is_xdist_controller(request_or_session) -> bool:
    """Return `True` if this is the xdist controller, `False` otherwise

    Note: this method also returns `False` when distribution has not been
    activated at all.

    :param request_or_session: the `pytest` `request` or `session` object
    """

def get_xdist_worker_id(request_or_session) -> str:
    """Return the id of the current worker ('gw0', 'gw1', etc) or 'master'
    if running on the controller node.

    If not distributing tests (for example passing `-n0` or not passing `-n` at all) also return 'master'.

    :param request_or_session: the `pytest` `request` or `session` object
    """

Identifying workers from the system environment

New in version UNRELEASED TBD FIXME

If the setproctitle package is installed, pytest-xdist will use it to update the process title (command line) on its workers to show their current state. The titles used are [pytest-xdist running] file.py/node::id and [pytest-xdist idle], visible in standard tools like ps and top on Linux, Mac OS X and BSD systems. For Windows, please follow setproctitle’s pointer regarding the Process Explorer tool.

This is intended purely as an UX enhancement, e.g. to track down issues with long-running or CPU intensive tests. Errors in changing the title are ignored silently. Please try not to rely on the title format or title changes in external scripts.

Uniquely identifying the current test run

New in version 1.32.

If you need to globally distinguish one test run from others in your workers, you can use the testrun_uid fixture. For instance, let’s say you wanted to create a separate database for each test run:

import pytest
from posix_ipc import Semaphore, O_CREAT

@pytest.fixture(scope="session", autouse=True)
def create_unique_database(testrun_uid):
    """ create a unique database for this particular test run """
    database_url = f"psql://myapp-{testrun_uid}"

    with Semaphore(f"/{testrun_uid}-lock", flags=O_CREAT, initial_value=1):
        if not database_exists(database_url):
            create_database(database_url)

@pytest.fixture()
def db(testrun_uid):
    """ retrieve unique database """
    database_url = f"psql://myapp-{testrun_uid}"
    return database_get_instance(database_url)

Additionally, during a test run, the following environment variable is defined:

• PYTEST_XDIST_TESTRUNUID: the unique id of the test run.

Accessing sys.argv from the master node in workers

To access the sys.argv passed to the command-line of the master node, use request.config.workerinput["mainargv"].

Specifying test exec environments in an ini file

You can use pytest’s ini file configuration to avoid typing common options. You can for example make running with three subprocesses your default like this:

[pytest]
addopts = -n3

You can also add default environments like this:

[pytest]
addopts = --tx ssh=myhost//python=python3.9 --tx ssh=myhost//python=python3.6

and then just type:

pytest --dist=each

to run tests in each of the environments.

Specifying “rsync” dirs in an ini-file

In a tox.ini or setup.cfg file in your root project directory you may specify directories to include or to exclude in synchronisation:

[pytest]
rsyncdirs = . mypkg helperpkg
rsyncignore = .hg

These directory specifications are relative to the directory where the configuration file was found.