.. image:: http://img.shields.io/pypi/v/pytest-xdist.svg

    :alt: PyPI version

    :target: https://pypi.python.org/pypi/pytest-xdist



.. image:: https://img.shields.io/conda/vn/conda-forge/pytest-xdist.svg

    :target: https://anaconda.org/conda-forge/pytest-xdist



.. image:: https://img.shields.io/pypi/pyversions/pytest-xdist.svg

    :alt: Python versions

    :target: https://pypi.python.org/pypi/pytest-xdist



.. image:: https://github.com/pytest-dev/pytest-xdist/workflows/build/badge.svg

    :target: https://github.com/pytest-dev/pytest-xdist/actions



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    :target: https://github.com/ambv/black



xdist: pytest distributed testing plugin

========================================



The `pytest-xdist`_ plugin extends pytest with some unique

test execution modes:



* test run parallelization_: if you have multiple CPUs or hosts you can use

  those for a combined test run.  This allows to speed up

  development or to use special resources of `remote machines`_.





* ``--looponfail``: run your tests repeatedly in a subprocess.  After each run

  pytest waits until a file in your project changes and then re-runs

  the previously failing tests.  This is repeated until all tests pass

  after which again a full run is performed.



* `Multi-Platform`_ coverage: you can specify different Python interpreters

  or different platforms and run tests in parallel on all of them.



Before running tests remotely, ``pytest`` efficiently "rsyncs" your

program source code to the remote place.  All test results

are reported back and displayed to your local terminal.

You may specify different Python versions and interpreters.



If you would like to know how pytest-xdist works under the covers, checkout

`OVERVIEW <https://github.com/pytest-dev/pytest-xdist/blob/master/OVERVIEW.md>`_.





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]





.. _parallelization:



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.



Making session-scoped fixtures execute only once

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^



``pytest-xdist`` is designed so that each worker process will perform its own collection and execute

a subset of all tests. This means that tests in different processes requesting a high-level

scoped fixture (for example ``session``) will execute the fixture code more than once, which

breaks expectations and might be undesired in certain situations.



While ``pytest-xdist`` does not have a builtin support for ensuring a session-scoped fixture is

executed exactly once, this can be achieved by using a lock file for inter-process communication.



The example below needs to execute the fixture ``session_data`` only once (because it is

resource intensive, or needs to execute only once to define configuration options, etc), so it makes

use of a `FileLock <https://pypi.org/project/filelock/>`_ to produce the fixture data only once

when the first process requests the fixture, while the other processes will then read

the data from a file.



Here is the code:



.. code-block:: python



    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





The example above can also be use in cases a fixture needs to execute exactly once per test session, like

initializing a database service and populating initial tables.



This technique might not work for every case, but should be a starting point for many situations

where executing a high-scope fixture exactly once is important.



Running tests in a Python subprocess

------------------------------------



To instantiate a python3.5 subprocess and send tests to it, you may type::



    pytest -d --tx popen//python=python3.5



This will start a subprocess which is run with the ``python3.5``

Python interpreter, found in your system binary lookup path.



If you prefix the --tx option value like this::



    --tx 3*popen//python=python3.5



then three subprocesses would be created and tests

will be load-balanced across these three processes.



.. _boxed:



Running tests in a boxed subprocess

-----------------------------------



This functionality has been moved to the

`pytest-forked <https://github.com/pytest-dev/pytest-forked>`_ plugin, but the ``--boxed`` option

is still kept for backward compatibility.



.. _`remote machines`:



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 :code:`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 :code:`--rsyncdir` directories

to be sent to the remote side.



.. note::



  For pytest to collect and send tests correctly

  you not only need to make sure all code and tests

  directories are rsynced, but that any test (sub) directory

  also has an :code:`__init__.py` file because internally

  pytest references tests as a fully qualified python

  module path.  **You will otherwise get strange errors**

  during setup of the remote side.





You can specify multiple :code:`--rsyncignore` glob patterns

to be ignored when file are sent to the remote side.

There are also internal ignores: :code:`.*, *.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





.. _`atonce`:

.. _`Multi-Platform`:





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`_.



.. _`xspec syntax`: http://codespeak.net/execnet/basics.html#xspec



.. _`socketserver.py`: https://raw.githubusercontent.com/pytest-dev/execnet/master/execnet/script/socketserver.py



.. _`execnet`: http://codespeak.net/execnet



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:



.. code-block:: python



    @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:



.. code-block:: python



    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 master, `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 'master' 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

        """





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:



.. code-block:: python



    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:



.. code-block:: ini



    [pytest]

    addopts = -n3



You can also add default environments like this:



.. code-block:: ini



    [pytest]

    addopts = --tx ssh=myhost//python=python3.5 --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:



.. code-block:: ini



    [pytest]

    rsyncdirs = . mypkg helperpkg

    rsyncignore = .hg



These directory specifications are relative to the directory

where the configuration file was found.



.. _`pytest-xdist`: http://pypi.python.org/pypi/pytest-xdist

.. _`pytest-xdist repository`: https://github.com/pytest-dev/pytest-xdist

.. _`pytest`: http://pytest.org