public void clears_all_subscriptions()
        {
            var subscriptions = new[]
            {
                ObjectMother.ExistingSubscription(),
                ObjectMother.ExistingSubscription(),
                ObjectMother.ExistingSubscription(),
                ObjectMother.ExistingSubscription()
            };

            _cache.LoadSubscriptions(subscriptions);
            _cache.ActiveSubscriptions.ShouldHaveTheSameElementsAs(subscriptions);

            _cache.ClearAll();
            _cache.ActiveSubscriptions.ShouldHaveCount(0);
        }