I recently ran into an issue where combining the DmarcDnsTestsMixin with WebAPITestCase was causing very unusual failure cases, which could be traced back to the cache. We have several things in our new expected queries which rely on the cache being populated with certain data, but the order in which things got initialized meant that the test case would populate the cache, and then this mixin would clear it. We'd then see extra queries popping up where we didn't expect them. I've moved the parent class `setUp` to happen after we've cleared the cache. Testing Done: Ran unit tests everywhere.