= Overview =
Parallel testing would be nice. Theres a bunch of things to do to make it work. See [[LEP/ParallelTesting|the LEP]] for constraints/goals/resourcing.

Known bugs/issues:
[[https://bugs.launchpad.net/launchpad-project/+bugs?field.tag=paralleltest|parallel test bugs]]

= LXC containers and parallel testing =

LXC containers combined with overlayfs (was [[http://en.wikipedia.org/wiki/Aufs|aufs]]) offer a pretty cheap way to get solid isolation - a great big hammer of a workaround for our existing globals (shared work dirs etc). William put together a proof of concept, Robert made that [[https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/807351/+attachment/2251192/+files/lxc-start-aufs|generic]], and it is now available, significantly refactored by Serge Hallyn, in lxc for Oneiric and later as "lxc-start-ephemeral".  That, combined with an updated .testr.conf given in the instructions below (a TODO is to offer profiles for testr) will let testr run tests in a temporary container. (e.g. testr -- -t stories/gpg will fire up an aufs container and run the stories/gpg tests inside it).

Be sure to export LP_LXC_BASE with the name of your lxc base container.

See [[Running/LXC]] for info on setting up  a  base container.

== Caveats ==

 * [[Bug:914365|If the base container is running it will be a disaster.]] Don't try.
 * aufs does not seem to permit deletes in some circumstances Bug:729338, so test fixtures which start by deleting a directory tree will fail if the directory tree exists. Known cases:
   * /var/tmp/testkeyserver.test
   * /var/lib/postgresql/8.4/main/postmaster.pid
   * /var/tmp/bazaar.launchpad.dev/mirrors
 * and conversely some need a tree:
 {{{
  File "/home/robertc/source/launchpad/lp-branches/working/lib/canonical/testing/layers.py", line 1775, in startSMTPServer
    handler = logging.FileHandler(log_file)
  File "/usr/lib/python2.6/logging/__init__.py", line 819, in __init__
    StreamHandler.__init__(self, self._open())
  File "/usr/lib/python2.6/logging/__init__.py", line 838, in _open
    stream = open(self.baseFilename, self.mode)
IOError: [Errno 2] No such file or directory: '/var/tmp/mailman/logs/smtpd'
}}} - this was because buildmailman had not been run in the base container.
 * If we leak a child process with a shared stdout/stderr sshd will not terminate, which will cause the testr test runner to look like it has hung. Bug:820726. sudo pkill memcached can be used to work around this.

== Workflow ==

=== One-time ===

 * [[Running/LXC|Set up an lxc instance]].
 * {{{sudo apt-get install testrepository}}} in your host instance.
 * In your source tree, run {{{testr init}}}.
 * Change your source tree's .testr.conf to the following:
 {{{
[DEFAULT]
test_command=lxc-start-ephemeral -o $LP_LXC_BASE -b $PWD -- xvfb-run -a $PWD/bin/test --subunit $IDOPTION $LISTOPT
test_id_option=--load-list $IDFILE
test_list_option=--list
}}}
 * You need a temp directory in your source tree to workaround bug Bug:808557
 {{{
mkdir temp
}}}

=== Working ===

 * Edit outside the container in your normal work area
 * Start the base container to do maintenance: make schema, bin/buildout
 {{{
lxc-start -n $basename -d
}}}
  * ssh to it
  * make schema
  * bin/buildout
  * shut it down.  In theory, {{{sudo poweroff}}} in your container should be sufficient.  Experience shows that sometimes this hangs.  Therefore, follow the poweroff with {{{lxc-stop -n <name>}}}.
    * Note that, also because of fragility, you may need to manually shutdown postgresql before stopping lxc, to get it to shutdown cleanly.

    * We may investigate creating a second test-only base instance in order to make this easier.

=== Running tests ===

 * Run tests with testr.  These commands assume that your lxc base instance (as created in the initial steps) is named lpdev.  If it is named something else, replace "lpdev" with that other name.  This also assumes that the base instance is shut down, as described in the previous section.
 All tests
 {{{
LP_LXC_BASE=lpdev TEMP=$(pwd)/temp testr run --parallel
}}}
 Some tests
 {{{
LP_LXC_BASE=lpdev TEMP=$(pwd)/temp testr run --parallel -- -t stories/gpg
}}}

 * XXX Note that the test count lies (layer setup and teardown confuses things in particular).  The yellow kanban board tracks a number of bugs in testr and related code pertinent to this.

== Tips ==

=== Accessing a LXC container from a buildbot slave ===
The default lxc container does not have any users you can use to login.  To get around this you can set a password for root in the host and copy the corresponding line from the host's {{{/etc/shadow}}} to that of the container.  You can then log into the container using the same password.  The steps are:
{{{
root@host> passwd root  # set password to, say, 'foo'
root@host> grep root /etc/shadow >> /var/lib/lxc/lptests/rootfs/etc/shadow
root@host> vi /var/lib/lxc/lptests/rootfs/etc/shadow  # Remove the orginal 'root' line with blank password information
}}}

Now, when you {{{lxc-start -n lptests}}} you can login as {{{root}}} using the password {{{foo}}}.