xdist: pytest distributed testing plugin¶
The pytest-xdist plugin extends
pytest with some unique
test execution modes:
- Looponfail: run your tests repeatedly in a subprocess. After each
pytestwaits until a file in your project changes and then re-runs the previously failing tests. This is repeated until all tests pass. At this point a full run is again performed.
- multiprocess Load-balancing: if you have multiple CPUs or hosts you can use them for a combined test run. This allows to speed up development or to use special resources of remote machines.
- 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.
Installation of xdist plugin¶
Install the plugin with:
easy_install pytest-xdist # or 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
Speed up test runs by sending tests to multiple CPUs¶
To send tests to multiple CPUs, type:
pytest -n NUM
Especially for longer running tests or tests requiring a lot of I/O this can lead to considerable speed ups.
Running tests in a Python subprocess¶
To instantiate a Python-2.7 subprocess and send tests to it, you may type:
pytest -d --tx popen//python=python2.7
This will start a subprocess which is run with the “python2.7” Python interpreter, found in your system binary lookup path.
If you prefix the –tx option value like this:
pytest -d --tx 3*popen//python=python2.7
then three subprocesses would be created and the tests will be distributed to three subprocesses and run simultanously.
Running tests in looponfailing mode¶
For refactoring a project with a medium or large test suite
you can use the looponfailing mode. Simply add the
pytest will run your tests. Assuming you have failures it will then
wait for file changes and re-run the failing test set. File changes are detected by looking at
looponfailingroots root directories and all of their contents (recursively). If the default for this value does not work for you you
can change it in your project by setting a configuration option:
# content of a pytest.ini or tox.ini file [pytest] looponfailroots = mypkg testdir
This would lead to only looking for file changes in the respective directories, specified relatively to the ini-file’s directory.
Sending tests to remote SSH accounts¶
Suppose you have a package
mypkg which contains some
tests that you can successfully run locally. And you also
have a ssh-reachable machine
you can ad-hoc distribute your tests by typing:
pytest -d --tx ssh=myhostpopen --rsyncdir mypkg mypkg
This will synchronize your
mypkg package directory
with a remote ssh account and then collect and run your
tests at the remote side.
You can specify multiple
to be sent to the remote side.
Sending tests to remote Socket Servers¶
Download the single-module socketserver.py Python program and run it like this:
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
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.
Specifying test exec environments in an ini file¶
pytest (since version 2.0) supports ini-style configuration. For example, you could make running with three subprocesses your default:
[pytest] addopts = -n3
You can also add default environments like this:
[pytest] addopts = --tx ssh=myhost//python=python2.7 --tx ssh=myhost//python=python2.6
and then just type:
to run tests in each of the environments.
Specifying “rsync” dirs in an ini-file¶
tox.ini 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.