Notifications dropdown with TinyScroll
From a once over:


Review your comments, some of them just take up space and are not very valuable:

// update scrollbar
$el.tinyscrollbar_update();

Indentation ( this might be because of copy pasting ) is off in your code, making it hard(er) to read
TEST.notif is a mouthful, I would just go for notifications
_el, _sum, _defaultVPHeight should all loose their underscore, they dont make sense. Also I would go either for the Spartan e or the full out element.
TEST.notif._notifOpen -> why notifOpen, it's already part of an object called notif, just call it open
Use lowerCamelCase consistently: tinyscrollbar_update -> tinyScrollbarUpdate


Other than that, your code is well structured and easy to follow.