[Zope-dev] Re: New test runner work

Stuart Bishop stuart at stuartbishop.net
Tue Aug 23 01:38:06 EDT 2005

Jim Fulton wrote:

> I'll note that I'm working on a newer test runner that I hope to use
> in Zope 2.9 and 3.2.  The new test runner is a nearly complete rewrite to
> provide:
> - A more flexible test runner that can be used for a variety of projects.
>   The current test runner has been forked for ZODB, Zope 3, and Zope 2.
>   That's why the Zope 3 version has features that are lacking in the Zope 2
>   version.
> - Support for "layers" of tests, so that it can handle unit tests and
>   functional tests.
> - A slightly better UI.
> - Tests (of the test runner itself :)
> See:
> http://svn.zope.org/zope.testing/trunk/src/zope/testing/testrunner.txt?view=log
> http://svn.zope.org/zope.testing/trunk/src/zope/testing/testrunner.py?view=log

Hi Jim.

I've been looking over this - fixing tests seems to take up a significant
amount of our time, so I might have some interesting use cases.

A large proportion of our tests use a relational database. Some of them want
an empty database, some of them want just the schema created but no data,
some of them want the schema created and the data. Some of them need the
component architecture, and some of them don't. Some of them need one or
more twisted servers running, some of them don't.

Note that we mix and match. We have 4 different types of database fixture
(none, empty, schema, populated), 2 different types of database connection
mechanisms (psycopgda, psycopg), 2 types of CA fixture (none, loaded), and
(currently) 4 states of external daemons needed. If we were to arrange this
in layers, it would take 56 different layers, and this will double every
time we add a new daemon, or add more database templates (e.g. fat for lots
of sample data to go with the existing thin).

As a way of supporting this better, instead of specifying a layer a test
could specify the list of resources it needs:

import testresources as r

class FooTest(unittest.TestCase):
    resources = [r.LaunchpadDb, r.Librarian, r.Component]

class BarTest(unittest.TestCase):
    resources = [r.EmptyDb]

class BazTest(unittest.TestCase):
    resources = [r.LaunchpadDb, r.Librarian]

The resources are pretty much identical to the current layers, in that
(after the test runner does some sorting fu), the run order can be optimized
to avoid setting up and tearing down resources unnecessarily. This would be
a big win for us - currently, we specify 'resources' by simply calling
various setup and teardown methods in the test case:

class FooTest(unittest.TestCase):
    def setUp(self):
    def tearDown(self):

Some other nice things could be done with the resources:

- If the setUp raises NotImplementedError (or whatever), tests using this
resource are skipped (and reported as skipped). This nicely handles tests
that should only be run in particular environments (Win32, Internet
connection, python.net installed etc.)

- If the setUp raises another exception, all tests using this resource fail.
The common case we see is 'database in use', where PostgreSQL does not let
us destroy or use as a template a database that has open connections to it.
Also useful for general sanity checking of the environment - no point
running the tests if we know they are going to fail or have skewed results.

- A resource should have a pretest and posttest hooks. pretest is used for
lightweight resource specific initialization (e.g. setUp creates a fresh
database from a dump and pretest initializes the connection pool). posttest
can be used to ensure tests cleaned up properly or other housekeeping (e.g.
issuing a rollback). This could also apply to layers in the current
environment. This eliminates tedious boilerplate from testcases.

- A resource could provide useful data to the test runner. For example, if a
resource says it doesn't use or lock any shared system resources, the test
runner could decide to run tests in parallel. Although a less blue sky use
would be specifying a dependancy on another resource.

On another note, enforcing isolation of tests has been a continuous problem
for us. For example, a developer registering a utility or otherwise mucking
around with the global environment and forgetting to reset things in
tearDown. This goes unnoticed for a while, and other tests get written that
actually depend on this corruption. But at some point, the order the tests
are run changes for some reason and suddenly test 500 starts failing. It
turns out the global state has been screwed, and you have the fun task of
tracking down which of the proceeding 499 tests screwed it. I think this is
a use case for some sort of global posttest hook. Perhaps this would be best
done by allowing people to write wrappers around the one-true-testrunner?
This seems to be the simplest way of allowing customization of the test runner:

def pretest(...):
def posttest(...):
if __name__ == '__main__':

Other policy could also be configured - e.g. 'Run these tests or tests using
this resource first. If any failures, don't bother running any more'. Or
'Stop running tests after 1 failure'. These sorts of policies are important
for us as we run our tests in an automated environment (we can't commit to
our trunk. Instead, we send a request to a daemon which runs the test suite
and commits on our behalf if the tests all pass).

Our full test suite currently takes 45 minutes to run and it is becoming an
issue. We need to speed them up, determine slow tests in need of pruning or
optimization, short circuit test runs and reduce test suite maintenance. So
I should be able to get time to help (although I need to look closer at the
SchoolTool and py.test runners to see if they are closer to what we need).

Stuart Bishop <stuart at stuartbishop.net>
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