Tests/fixture loading should invalidate cache.
I'm still investigating further, but it seems that I have tests failing because the fixtures that are being loaded as part of the test setup are not being reflected in the returned data when the johnny-cache middlewares are installed.
I think it is because the fixtures are loaded in without the cache being invalidated. Loading fixtures should invalidate the cache.
There are two ways that fixtures are loaded, that I am aware of: the management command loaddata, and as part of the test creation in django.