Ember.js Array Obeserver

I am writing an observer on an Ember Array testArrayObserver: function(){

....

}.observes('testArray.@each'),

Now, this observer will hit whenever any changes are made to array may an element gets added or removed.

I want to asked that when ever this observer hits, can we know the reason i.e. weather adding element to array invoked the observer or removing an element from the array invoked the observer.

Please give specific answers.

Regards

Dn