Package: pytest-xdist-forked
xdist: pytest distributed testing pluginThepytest-xdistplugin extends pytest with some unique
test execution modes:test runparallelization: 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 ofremote 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-Platformcoverage: you can specify different Python interpreters
or different platforms and run tests in parallel on all of them.Before running tests remotely,pytestefficiently “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, checkoutOVERVIEW.InstallationInstall the plugin with:pip install pytest-xdistor use the package in develop/in-place mode with
a checkout of thepytest-xdist repositorypip install --editable .Speed up test runs by sending tests to multiple CPUsTo send tests to multiple CPUs, type:pytest -n NUMEspecially 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 toautofor 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-restartoption to limit the number of workers that can
be restarted, or disable restarting altogether using--max-worker-restart=0.By default, the-noption 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 bymodulefortest functionsand
byclassfortest 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 version1.19.--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 version1.21.Making session-scoped fixtures execute only oncepytest-xdistis 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 examplesession) will execute the fixture code more than once, which
breaks expectations and might be undesired in certain situations.Whilepytest-xdistdoes 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 fixturesession_dataonly once (because it is
resource intensive, or needs to execute only once to define configuration options, etc), so it makes
use of aFileLockto 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:importjsonimportpytestfromfilelockimportFileLock@pytest.fixture(scope="session")defsession_data(tmp_path_factory,worker_id):ifnotworker_id:# not executing in with multiple workers, just produce the data and let# pytest's fixture caching do its jobreturnproduce_expensive_data()# get the temp directory shared by all workersroot_tmp_dir=tmp_path_factory.getbasetemp().parentfn=root_tmp_dir/"data.json"withFileLock(str(fn)+".lock"):iffn.is_file():data=json.loads(fn.read_text())else:data=produce_expensive_data()fn.write_text(json.dumps(data))returndataThe 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 subprocessTo instantiate a python3.5 subprocess and send tests to it, you may type:pytest -d --tx popen//python=python3.5This will start a subprocess which is run with thepython3.5Python interpreter, found in your system binary lookup path.If you prefix the –tx option value like this:--tx 3*popen//python=python3.5then three subprocesses would be created and tests
will be load-balanced across these three processes.Running tests in a boxed subprocessThis functionality has been moved to thepytest-forkedplugin, but the--boxedoption
is still kept for backward compatibility.Sending tests to remote SSH accountsSuppose you have a packagemypkgwhich contains some
tests that you can successfully run locally. And you
have a ssh-reachable machinemyhost.  Then
you can ad-hoc distribute your tests by typing:pytest -d --tx ssh=myhostpopen --rsyncdir mypkg mypkgThis will synchronize yourmypkgpackage directory
to a remote ssh account and then locally collect tests
and send them to remote places for execution.You can specify multiple--rsyncdirdirectories
to be sent to the remote side.NoteFor 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__init__.pyfile because internally
pytest references tests as a fully qualified python
module path.You will otherwise get strange errorsduring setup of the remote side.You can specify multiple--rsyncignoreglob 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 ServersDownload the single-modulesocketserver.pyPython program
and run it like this:python socketserver.pyIt 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 mypkgRunning tests on many platforms at onceThe basic command to run tests on multiple platforms is:pytest --dist=each --tx=spec1 --tx=spec2If 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 thexspec syntax.Identifying the worker process during a testNew in version 1.15.If you need to determine the identity of a worker process in
a test or fixture, you may use theworker_idfixture to do so:@pytest.fixture()defuser_account(worker_id):""" use a different account in each xdist worker """return"account_%s"%worker_idWhenxdistis disabled (running with-n0for example), thenworker_idwill 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-n4is given in the command-line.The information about the worker_id in a test is stored in theTestReportas
well, under theworker_idattribute.Acessingsys.argvfrom the master node in workersTo access thesys.argvpassed to the command-line of the master node, userequest.config.workerinput["mainargv"].Specifying test exec environments in an ini fileYou 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=-n3You can also add default environments like this:[pytest]addopts=--tx ssh=myhost//python=python3.5 --tx ssh=myhost//python=python3.6and then just type:pytest --dist=eachto run tests in each of the environments.Specifying “rsync” dirs in an ini-fileIn atox.iniorsetup.cfgfile in your root project directory
you may specify directories to include or to exclude in synchronisation:[pytest]rsyncdirs=. mypkg helperpkgrsyncignore=.hgThese directory specifications are relative to the directory
where the configuration file was found.