Characterization tests using Mocha and expect.js to understand how Underscore.js' tap function works

javascript_underscore_tap_characterization_spec.js

var _ = require("underscore"),
  send = require("allong.es").allong.es.send,
  expect = require("expect.js");

// Characterization tests using Mocha and expect.js to understand how
// underscore.js' tap function works 
// See http://comp-phil.blogspot.com/2014/03/bird-watching-with-javascript-kestrel.html 

describe("Verify that we understand how tap works", function(){
  describe("Call tap with a value", function(){
    it("Give a string and a function which does nothing the string will be the same", function(){
      expect(_.tap("Mr. Jack", function(){})).to.be.equal("Mr. Jack");
    }),
    it("Given a value and a function which increments a value the value will increment on each call", function(){
      var counter = 0,
        increment = function(){counter++;},
        peek = function(){return _.tap("Look here", increment);};
      expect(counter).to.be.equal(0);
      expect(peek()).to.be.equal("Look here");
      expect(counter).to.be.equal(1);
      peek();
      expect(counter).to.be.equal(2);
    });
  }),
  describe("Call tap with an array", function(){
    var array = [1, 2, 3, 4, 5];
    beforeEach(function(done){
      array = [1, 2, 3, 4, 5];  // to reset before each test case
      done();
    });

    it("Given an array and a function which does nothing array will be the same", function(){
      expect(_.tap(array, function(){})).to.be.eql(array);
    }),
    it("Given an array applying pop against it in a tap will remove the last value it", function(){
      expect(_.tap(array, send("pop"))).to.be.eql([1, 2, 3, 4]);
    }),
    it("Given an array applying push against it will add the value to the array", function(){
      expect(_.tap(array, send("push", 6))).to.be.eql([1, 2, 3, 4, 5, 6]);
    });
  });
});

See my blog post which goes with this gist: http://comp-phil.blogspot.com/2014/03/bird-watching-with-javascript-kestrel.html