@Test
    public void testCreateDefaultVisitorControlHandlerIfNoneGiven() {
        MockSender sender = new MockSender();
        MockReceiver receiver = new MockReceiver();
        MockAsyncTaskExecutor executor = new MockAsyncTaskExecutor();
        VisitorParameters params = createVisitorParameters("");
        MessageBusVisitorSession visitorSession = createVisitorSession(
                sender, receiver, executor, params);
        assertNotNull(params.getControlHandler());
    }
Test that using an id.user=foo selection only tries to visit a single
superbucket for that user.
documentapi/src/test/java/com/yahoo/documentapi/messagebus/MessageBusVisitorSessionTestCase.java