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.
• --boxed: (not available on Windows) run each test in a boxed subprocess to survive SEGFAULTS or otherwise dying processes
• --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.

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

python setup.py develop

Usage examples

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 IO 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 slave and report the failure as usual. You can use the --max-slave-restart option to limit the number of slaves that can be restarted, or disable restarting altogether using --max-slave-restart=0.

Running tests in a Python subprocess

To instantiate a python2.5 sub process and send tests to it, you may type:

py.test -d --tx popen//python=python2.5

This will start a subprocess which is run with the "python2.5" Python interpreter, found in your system binary lookup path.

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

--tx 3*popen//python=python2.5

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

Running tests in a boxed subprocess

If you have tests involving C or C++ libraries you might have to deal with tests crashing the process. For this case you may use the boxing options:

py.test --boxed

which will run each test in a subprocess and will report if a test crashed the process. You can also combine this option with running multiple processes to speed up the test run and use your CPU cores:

py.test -n3 --boxed

this would run 3 testing subprocesses in parallel which each create new boxed subprocesses for each test.

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.

Note

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

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 worker_id attribute.

New in version 1.15.

Specifying test exec environments in an ini file

pytest (since version 2.0) supports ini-style cofiguration. 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=python2.5 --tx ssh=myhost//python=python2.6

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.