1_suite.js

// #suite is a helper method to more concisely list
// #describe groups. Example usage:
//
// suite("Examples", {
//
//   "before" : function(){
//     // ... setup
//   },
//
//   "should one" : function(){
//     // ... top level spec
//   },
//
//   "should two" : function(){
//     // ... top level spec
//   }
//
//   "describing Nested" : {
//
//     "should one" : function(){
//       // ... nested spec
//     },
//
//     "should two" : function(){
//       // ... nested spec
//     }
//
//   }
//
// });
var SuiteWalker = function(desc, object){
  var description = desc,
      blocks      = object;

  function run(){
    describe(description, function(){
      var key;

      for(key in blocks){
        var parts   = key.split(" "),
            keyword = parts[0],
            block   = blocks[key];

        switch(keyword){

          case 'scenario':
          case 'describing':
            var desc   = parts.slice(1, parts.length).join(" ");
            var walker = new SuiteWalker(desc, block);

            walker.run();
          break;

          case 'before':
            beforeEach(block);
          break;

          case 'after':
            afterEach(block);
          break;

          case 'it':
          case 'should':
            it(key, block);
          break;

          case 'pending':
            xit(key, block);
          break;

          default:
            throw "Can't determine context to call the current keyword '" + keyword + "' in."
          break;

        }
    }
    });
  };

  return {
    run : run
  }
};

var suite = function(desc, blocks){
  var walker = new SuiteWalker(desc, blocks);

  walker.run();
};

2_calculator.js

var Calculator = function(){
  
  function add(one, two){
    return one + two;
  };

  function subtract(one, two){
    return one - two;
  };

  return {
    add : add,
    subtract : subtract
  }
};

3_before.js

describe("Calculator", function(){
  var result,
      calculator = new Calculator();

  describe("add", function(){

    beforeEach(function(){
      result = 0;
    });

    it("should perform addition", function(){
      result = calculator.add(2, 2);
      expect(result).toEqual(4);
    })

  });

  describe("subtract", function(){

    beforeEach(function(){
      result = 0;
    });

    it("should perform subtraction", function(){
      result = calculator.subtract(4, 2);
      expect(result).toEqual(2);
    })

  });

});

4_after.js

suite("Calculator", {


  before : function(){
    this.result     = null;
    this.calculator = new Calculator();
  },


  "describing #add" : {


    before : function(){
      this.result = 0;
    },


    "should perform addition" : function(){
      this.result = this.calculator.add(2, 2);
      expect(this.result).toEqual(4);
    }


  },


  "describing #subtract" : {


    before : function(){
      this.result = 0;
    },


    "should perform subtraction" : function(){
      this.result = this.calculator.subtract(4, 2);
      expect(this.result).toEqual(2);
    }


  }


});

Nice work mate, nicer to read