Package: qieman-xdist
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-xdistTo usepsutilfor detection of the number of CPUs available, install thepsutilextra:pip install pytest-xdist[psutil]Speed up test runs by sending tests to multiple CPUsTo send tests to multiple CPUs, use the-n(or--numprocesses) option:pytest -n NUMCPUSPass-nautoto 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-restartoption
to limit the number of worker restarts that are allowed, or disable restarting
altogether using--max-worker-restart0.By default, using--numprocesseswill send pending tests to any worker that
is available, without any guaranteed order. You can change the test
distribution algorithm this with the--distoption. It takes these values:--distno: The default algorithm, distributing one test at a time.--distloadscope: Tests are grouped bymodulefortest functionsand byclassfortest 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.--distloadfile: 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 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):ifworker_id=="master":# 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".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-n4is given in the command-line.The information about the worker_id in a test is stored in theTestReportas
well, under theworker_idattribute.Since version 2.0, the following functions are also available in thexdistmodule:defis_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
    """defis_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
    """defget_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 runNew in version 1.32.If you need to globally distinguish one test run from others in your
workers, you can use thetestrun_uidfixture. For instance, let’s say you
wanted to create a separate database for each test run:importpytestfromposix_ipcimportSemaphore,O_CREAT@pytest.fixture(scope="session",autouse=True)defcreate_unique_database(testrun_uid):""" create a unique database for this particular test run """database_url=f"psql://myapp-{testrun_uid}"withSemaphore(f"/{testrun_uid}-lock",flags=O_CREAT,initial_value=1):ifnotdatabase_exists(database_url):create_database(database_url)@pytest.fixture()defdb(testrun_uid):""" retrieve unique database """database_url=f"psql://myapp-{testrun_uid}"returndatabase_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.Accessingsys.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.