The idea of splitting integration from unittests is good in theory
but leads to a lot of mental overhead. Besides whenever a tests
interacts with a database it isn't a unittest anyway.

Better to use filenames which are commonly used in the python word then
custom ones.

Since there is no way to override SlugField and AutoSlugField in existing Oscar models, it was decided to pass `allow_unicode` parameter if this setting enable. This allows to achieve backwards compatibility with Django versions under 1.9, when this parameter was not supported yet. If parameter specified in the field expliticly - we do not override it, which allow to control slug fields individually in a normal way. For the reasons, explained above, standard SlugField was replaced with a custom one with the single slight change - control over `allow_unicode` parameter by the mentioned setting.