xdist: pytest distributed testing plugin
The pytest-xdist plugin extends py.test with some unique test execution modes:
- 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.
- multiprocess Load-balancing: 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.
- 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.
Install the plugin with:
easy_install pytest-xdist # or pip install pytest-xdist
or use the package in develope/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:
py.test -n NUM
Especially for longer running tests or tests requiring a lot of IO this can lead to considerable speed ups.
Running tests in a Python subprocess
To instantiate a python2.4 sub process and send tests to it, you may type:
py.test -d --tx popen//python=python2.4
This will start a subprocess which is run with the "python2.4" Python interpreter, found in your system binary lookup path.
If you prefix the --tx option value like this:
then three subprocesses would be created and tests will be load-balanced across these three processes.
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.
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:
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.
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:
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.