Test for expected timeout in mocha

I have a Faye publish/subscribe server that sends a message to new subscribers only if a message has already been sent to the other subscribers. I am using mocha for unit testing.

This test works to confirm the basic functionality:

    it('should send a special message to new subscribers', function(done){
        testerPubSub.setLastJsonContent('some arbitrary content');
        var subscription = client.subscribe("/info", function(message) {
            assert.equal(true, message.text.indexOf('some arbitrary content') !== -1, 'new subscriber message not sent');
            done();
        });
        subscription.cancel();
    });

But I would now like to test the case where there has not been a message sent to previous subscribers. This test would be something like:

    it('should not send a special message to new subscribers if no data has been retrieved', function(done){
        testerPubSub.setLastJsonContent(null);
        var messageReceived = false;
        var subscription = client.subscribe("/sales", function(message) {
            messageReceived = true;
        });

        ////need to magically wait 2 seconds here for the subscription callback to timeout

        assert.equal(false, messageRecieved, 'new subscriber message received');
        subscription.cancel;
        done();
    });

Of course, the magic sleep function is problematic. Is there a better way to be doing this sort of "I expect the callback to never get fired" test?

Thanks, Mike