Mock django db

[donkirkby]

Recreating pull request #20 after it got rebasted.

Remaining work:

• Move stuff from utils to a separate mocks.py module.
• Delete mock_setup.py from example.
• Clarify docs on monkey_patch_test_db(), and how it's used in example, including @skipIfDBFeature('is_mocked') decorator.
• Test it with pytest-django.
• Document all three Django helpers in source code to describe when they are used.

[codecov-io]

Current coverage is 100% (diff: 100%)

Merging #23 into master will not change coverage

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[donkirkby]

OK, this is ready for merging, I think.

Feel free to comment out the pytest runs in tox.ini, if you think it's too much. However, I added them when I realized that I had broken the example project for pytest by moving test_api.py and test_views.py into the Django default of tests.py. It seems like it's too easy to break stuff if you don't actually run it.

Because I added a requirement for pytest-django, you'll need to run tox --recreate the first time.

[stphivos]

Cool thanks it looks good! Yeah let's keep the additional runs in tox.ini. 👍