A software development process that relies on the repetition of a very short development cycle: first the developer writes a failing automated test case that defines a desired improvement or new function, then produces code to pass that test and finally refactors the new code to acceptable standards.

ref: http://en.wikipedia.org/wiki/Test-driven_development

Introducing BDD : http://blog.dannorth.net/introducing-bdd/

"...where to start, what to test and what not to test, how much to test in one go, what to call their tests, and how to understand why a test fails."

Basically use language/terminology that everyone on the project understands; using a pattern (e.g. Given, When, Then.) to test expected behavior.

"Developers discovered it could do at least some of their documentation for them, so they started to write test methods that were real sentences."

1. Add a test
2. Run all tests and see if the new one fails
3. Write some code
4. Run the automated tests and see them succeed
5. Refactor code
6. Repeat

"Test-driven development constantly repeats the steps of adding test cases that fail, passing them, and refactoring. Receiving the expected test results at each stage reinforces the programmer's mental model of the code, boosts confidence and increases productivity."

Could have used…

              var today = new Date(); 
              if (today.getDay() == 0 || today.getDay() == 6) { 
                $('#dr_billingContainer h3:eq(0)').html('Billing Information');
              }
            

…Instead chose to make a jQuery plugin that acts as a utility method that can easily be reused for other sites

              /* namespace */
              module('namespace check');
              test('is dr a global variable.',function(){
                  expect(1);
                  ok( window.dr, 'dr namespace is present');
              });
            

              if (!window.dr) { var dr = {}; } // using dr as namespace
            

              module("dr.isWeekend() utility fn uses jQuery", {
                setup: function() {
                  dr.date = new Date();
                  dr.weekdays = [1,2,3,4,5];
                  dr.weekends = [0,6];
                },
                teardown: function() {
                  delete dr.date;
                  delete dr.weekdays;
                  delete dr.weekends;
                }
              });
            

              test("dr.isWeekend() expects argument of object type Date", function(){
                  // Arrange - use setup() for dr.date
                  var testPluginDefault;
                  // Act
                  testPluginDefault = dr.isWeekend();
                  // Assert
                  expect(1);
                  notStrictEqual( testPluginDefault, 'error', "Plugin does not return 'error' comparing with notStrictEqual");
              });
            

              (function($) {

              $.fn.isWeekend = function(options) {
                  var defaults = {};
                  opts = $.extend({},defaults, options);
                  // return this.each(function() { 
                      // code plugin here ...
                  // });
              };
              dr.isWeekend = $.fn.isWeekend;

              })(jQuery);
            

              test("dr.isWeekend() expects argument of object type Date", function(){
                  // Arrange - use setup() for dr.date
                  var testPluginDefault;
                  // Act
                  testPluginDefault = dr.isWeekend();
                  // Assert
                  expect(1);
                  notStrictEqual( testPluginDefault, 'error', "Plugin does not return 'error' comparing with notStrictEqual");
              });
            

              $.fn.isWeekend = function(options) {
                  var defaults, opts;
                  defaults = { date: new Date() };
                  opts = $.extend({},defaults, options);
                  if (Object.prototype.toString.call(opts.date) === '[object Date]') {
                      opts.dateOk = true;
                  } else {
                      return 'invalid';
                  }
              };
            

              // Act
              // ...
              testPluginTrue = dr.isWeekend({ date: dr.date });
              // Assert
              expect(3);
              // ...
              notStrictEqual( testPluginTrue, 'invalid', "Plugin does not return 'invalid' comparing with notStrictEqual");