
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.  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, "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 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


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 I/O
this can lead to considerable speed ups.


Running tests in a Python subprocess
------------------------------------

To instantiate a Python-2.4 subprocess 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:

   py.test -d --tx 3*popen//python=python2.4

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 "--f" option:

   py.test -f

and py.test 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, setup.cfg 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 "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 with a remote ssh
account and then collect and run your tests at the remote side.

You can specify multiple "--rsyncdir" directories 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:

   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.


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=python2.5 --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.
