[Python-ideas] Test Class setup and teardown in unittest (original) (raw)

Mark Roddy markroddy at gmail.com
Thu Jan 21 01:38:29 CET 2010

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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

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