'Test that setting an existing field changes the value'

def test_set_existing_field(self):

    with self.assertNumQueries(1):
        self.kvs.set(self.key_factory('existing_field'), 'new_value')
    self.assertEquals(1, self.storage_class.objects.all().count())
    self.assertEquals('new_value', json.loads(self.storage_class.objects.all()[0].value))
