Testing examples should use django.utils.TestCase

[jcspray@…]

The 'Testing Django applications page' (​https://docs.djangoproject.com/en/dev/topics/testing/) gives many examples of tests using unittest2.TestCase directly rather than django.test.TestCase.

For the DB to be reset between tests it is essential to use django.test.TestCase, and that is not made at all obvious in this documentation.

• At least: a prominent warning should be present about the fact that DB side effects are possible when using unittest2.TestCase
• Preferably: the examples should use django.utils.TestCase since it is a safer default.

[Aymeric Augustin]

Within Django itself, the convention is to use unittest.TestCase for tests that don't need django.test.TestCase, although I'm not entirely sure about the reason (performance?).

I'd like to see a benchmark before recommending to use django.test.TestCase unconditionally.

[Preston Holmes]

As the differences are already documented: ​https://docs.djangoproject.com/en/dev/topics/testing/#testcase

perhaps it would suffice just to have a quick note about database effects and a forward link to that section of the docs at the bottom of the introduction "writing unit tests" (just before the "writing doctests" section)

​https://docs.djangoproject.com/en/dev/topics/testing/#writing-unit-tests.

[Tim Graham]

I think a warning is definitely appropriate. In fact, the current example has database side effects.

[Tim Graham <timograham@…>]

In 7df03268a467a9aec9c4c574c85317a738ca33ae:

Fixed #17312 - Warned about database side effects in tests.

Thanks jcspray for the suggestion.

[Tim Graham <timograham@…>]

In 2545dc59bf44131a1f60f7393f29f025939f3a09:

[1.5.x] Fixed #17312 - Warned about database side effects in tests.

Thanks jcspray for the suggestion.

Backport of 7df03268a467a9aec9c4c574c85317a738ca33ae from master.