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

Michael Foord fuzzyman at voidspace.org.uk
Thu Jan 21 15:16:00 CET 2010

On 21/01/2010 04:03, Robert Collins wrote:
> On Wed, 2010-01-20 at 22:32 -0500, Mark Roddy wrote:
>>> I think that this is the wrong approach to the problem:
>>>   - class scope for such fixtures drives large test classes, reduces
>>> flexability
>> I can see how this could arise, but it has not been my experience (I
>> have a class setup system I've been using for a little while).  A
>> setUp method alone can be abused to create large inflexible tests.  I
>> think the answer to this is good documentation that clearly states
>> that abusing the functionality can lead to shooting oneself in the
>> foot.
> Yes, setUp and tearDown can be problematic as well. Junit which has has
> setUp and setUpClass a long time has recently
> (http://kentbeck.github.com/junit/doc/ReleaseNotes4.7.html) added a
> system called Rules which is similar to testresources (though the fine
> detail is different). The key elements are the same though:
>   - rules are their own hierarchy
>   - rules are added to tests not part of the test specific code
>   - framework takes care of bringing up and taking down rules.

Right, they *can* be problematic but they can also be extremely useful 
if not abused. My feeling is that the same is true of setupClass and 

Replacing them with a more complex mechanism is not necessarily a win, 
although a more complex mechanism for more complex use cases is 
justified (although it doesn't necessarily *need* to be in the standard 

> [snip...]
>>> I'd much much much rather see e.g. testresources integrated into the
>>> core allowing fixtures to be shared across test instances in a way that
>>> doesn't prohibit their use with concurrent testing, doesn't make it
>>> awkward to do it across multiple classes. I'm happy to make any
>>> [reasonable] changes (including license) to testresources to make it
>>> includable in the stdlib if that's of interest.
>> A pretty good approach for a complicated setup, but in a simple case
>> where you only need a line or two it seems like a lot of boiler plate
>> to get the job done.  Though I'll look into this library a little more
>> as I am not intimately familiar with it at the moment.
> If you only need a line or two, its hard to justify setUpClass being
> used :).
> Anyhow, its really not much boilerplate:
> class MyResource(TestResource):
>      def make(self, deps):
>          # line or two
>          return thing
> I am considering adding a helper to testresources:
> def simple_resource(maker, cleaner):
>      class MyResource(TestResource):
>          def make(self, deps):
>              return maker(deps)
>          def clean(self, resource):
>              cleaner(resource)
>      return MyResource
> which would make the boilerplate smaller still.

This doesn't show how testresources is used in conjunction with unittest 
- can you give a minimal *self contained* example please.



> Cheers,
> Rob


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