@Test
    public void testDeleteSubscription() throws Exception
    {
        // Setup test fixture.
        final CachingPubsubPersistenceProvider provider = new CachingPubsubPersistenceProvider();
        final Node mockNode = Mockito.mock(Node.class);
        Mockito.lenient().when(mockNode.getUniqueIdentifier()).thenReturn(new Node.UniqueIdentifier("mock-service-1", "mock-node-a"));
        final JID subscriber = new JID("test-user-1", "example.org", null);
        final String subscriptionId = "test-subscription-id-" + StringUtils.randomString(7);
        final NodeSubscription subscription = new NodeSubscription(mockNode, subscriber, subscriber, NodeSubscription.State.subscribed, subscriptionId);

        // Execute system under test.
        provider.removeSubscription(subscription);

        // Verify results.
        final List<CachingPubsubPersistenceProvider.NodeOperation> pending = provider.nodesToProcess.computeIfAbsent(mockNode.getUniqueIdentifier(), id -> new ArrayList<>());
        assertEquals(1, pending.size());

        final CachingPubsubPersistenceProvider.NodeOperation nodeOperation = pending.get(0);
        assertEquals(mockNode.getUniqueIdentifier(), nodeOperation.node.getUniqueIdentifier());
        assertEquals(CachingPubsubPersistenceProvider.NodeOperation.Action.REMOVE_SUBSCRIPTION, nodeOperation.action);
        assertEquals(subscriptionId, nodeOperation.subscription.getID());
        assertNull(nodeOperation.affiliate);

        assertEquals(0, provider.itemsPending.size());
        assertEquals(0, provider.itemsToAdd.size());
        assertEquals(0, provider.itemsToDelete.size());
    }
Asserts that an invocation of {@link CachingPubsubPersistenceProvider#removeSubscription(NodeSubscription)} causes a corresponding
operation to be scheduled.
xmppserver/src/test/java/org/jivesoftware/openfire/pubsub/CachingPubsubPersistenceProviderSubscriptionOperationsTest.java