Underscore is an awesome functional javascript library but I think it needs a flush feature so we can easily test our applications that use it.
A underscore.flush method would allow you to test the different cases without having to make your unit tests slow. This could work similar to angular.js's $httpBackend.flush().
Heres an implementation of what I mean.
https://gist.github.com/stephennancekivell/5899425