call-list-spec.js

describe('CallList', function() {
  var subject;
  beforeEach(function() {
    subject = new CallList({items: ['A','B','C']});
  });

  describe("#moveUp", function() {
    context("moving up C", function() {
      beforeEach(function() {
        subject.moveUp('C');
      });

      it("places it above B", function() {
        expect(subject.get('items')).toEqual(['A','C','B']);
      });
    });

    context("moving up B", function() {
      beforeEach(function() {
        subject.moveUp('B');
      });

      it("places B above A", function() {
        expect(subject.get('items')).toEqual(['B','A','C']);
      });
    });

    context("moving up A", function() {
      beforeEach(function() {
        subject.moveUp('A');
      });

      it("leaves the items as they were", function() {
        expect(subject.get('items')).toEqual(['A','B','C']);
      });
    });
  });
});

call-list.js

window.CallList = Backbone.Model.extend({
  moveUp: function(item) {
    var items = this.get('items');
    var index = _(items).indexOf(item) - 1;
    if(index >= 0) {
      items.splice(index,2,item,items[index]);
    }
  }
});