By default, disable all caching in tests, to preserve test independence.
In order to enable caching, inherit from CacheSetupMixin, and specify
which cache configuration is needed.

[EV-32]

The TestCase API doesn't accept arguments, so passing arguments for some
TestCase subclasses makes adding new inheritance/mixins tricky. Instead,
prefer configuration via class attributes for TestCases.

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar