GraphQLTestCase inherits from Django's TestCase, which requires a database

I'm using Django in a project which doesn't use a database, however I can't use graphene-django's `GraphQLTestCase`, as it inherits from Django's `TestCase` (I'm using `SimpleTestCase` elsewhere).

Could `GraphQLTestCase` extend from `SimpleTestCase`? Or if this is not desired because the most common usage does involve a database, could we move the methods to a mixin, so I can use this in combination with `SimpleTestCase`?

I can't see anything in `GraphQLTestCase` which actually requires a Django database to be configured.