[Python-ideas] Test Class setup and teardown in unittest

[Mark Roddy]

Earlier this week on the Testing In Python list, there was a
discussion on how to execute a setup and/or teardown for a single test
class instead of for each test fixture on the class (see the 'setUp
and tearDown behavior' thread).  I have had to deal with situation
myself before, and I am obviously not the only one (since I did not
initiate the thread).  As such I'd like to propose adding a class
level setup and tear down method the unittest TestCase class.

Rationale:
Test cases can at times require the setup of expensive resources.
This is often the case when implementing integration testing.  Having
to perform this setup for each fixture can prohibited for large number
of fixtures and/or for resources that are expensive to setup.  For
example, I have several hundred integration tests that hit a live
database.  If I create the connection object for each fixture, most of
the tests fail due to the maximum connection limit being reached.  As
a work around, I create a connection object once for each test case.
Without such functionality built in, the common idiom runs along these
lines:

class MyTest(TestCase):

    def setUp(self):
        if not self.ClassIsSetup:
            self.setupClass()
            self.ClassIsSetup=True

While this achieves the desired functionality, it is unclear due to
conditional setup code and is also error prone as the same code
segment would need to appear in every TestCase requiring the
functionality.  Having a class wide setup and teardown function that
implementers of test cases can override would make the code/intent
more clear and alleviate the need to implement test case functionality
when the user should be focusing on writing tests.

I emailed Michael Foord about some of his comments in the TIP thread
and to ask if he would be interested in a patch adding this
functionality, and I have included his response below.  I would like
to hear people's comments/suggestions/ideas before I start working on
said patch.

Thanks,
-Mark


Michael Foord's Email:
=======================================
I would certainly be interested in adding this to unittest.

It needs a discussion of the API and the semantics:

* What should the methods be called? setup_class and teardown_class or
setupClass and teardownClass? For consistency with existing methods
the camelCase should probably be used.
* If the setupClass fails how should the error be reported? The
*easiest* way is for the failure to be reported as part of the first
test
* Ditto for teardownClass - again the easiest way is for it to be
reported as a failure in the last test
* If setupClass fails then should all the tests in that class be
skipped? I think yes.

Also details like ensuring that even if just a single test method from
a class is run the setupClass and teardownClass are still run. It
probably needs to go to python-dev or python-ideas for discussion.

All the best,

Michael