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XDIST: PYTEST DISTRIBUTED TESTING PLUGIN


The pytest-xdist plugin extends py.test 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 py.test 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, py.test 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.


Installation

Install the plugin with:

    pip install pytest-xdist

or use the package in develop/in-place mode with a checkout of the
pytest-xdist repository :

    pip install --editable .


Speed up test runs by sending tests to multiple CPUs

To send tests to multiple CPUs, type:

    py.test -n NUM

Especially for longer running tests or tests requiring a lot of I/O this
can lead to considerable speed ups. This option can also be set to auto
for automatic detection of the number of CPUs.

If a test crashes the interpreter, pytest-xdist will automatically
restart that worker and report the failure as usual. You can use the
--max-worker-restart option to limit the number of workers that can be
restarted, or disable restarting altogether using
--max-worker-restart=0.

By default, the -n option will send pending tests to any worker that is
available, without any guaranteed order, but you can control this with
these options:

-   --dist=loadscope: tests will be grouped by MODULE for _test
    functions_ and by CLASS for _test methods_, then each group will be
    sent to an available worker, guaranteeing 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. Currently the groupings can't
    be customized, with grouping by class takes priority over grouping
    by module. This feature was added in version 1.19.
-   --dist=loadfile: tests will be grouped by file name, and then will
    be sent to an available worker, guaranteeing that all tests in a
    group run in the same worker. This feature was added in version
    1.21.


Running tests in a Python subprocess

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

    py.test -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.


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:

    py.test -d --tx ssh=myhostpopen --rsyncdir mypkg mypkg

This will synchronize your mypkg package directory to an 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.

For py.test 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 __init__.py file because internally py.test
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 --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:

    py.test -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:

    py.test --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".

Additionally, worker processes 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.


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=python3.5 --tx ssh=myhost//python=python3.6

and then just type:

    py.test --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.
