Faking dates in jasmine

date.js

/* Faking dates
 * when I need to fake a date, my preferred way is to introduce a new 
 * production method that returns the date I need (usually I need the 
 * current date, but it could just as well forward arguments). Once
 * we have it, we can spy on it just like we could anything else.
 * **/
window.currentDate = function() { return new Date(); };

window.newAllyMcbealTonight = function(){
  return currentDate().getFullYear() == 1998;
};

date_spec.js

describe(".currentDate", function() {
  it("returns the current date", function() {
    expect(window.currentDate()).toBeWithinASecondOf(new Date());
  });
});

describe("the 90s",function(){
  beforeEach(function(){
    fakeDate(1998,11,10);
  });

  it("has a new ally mcbeal tonight!",function(){
    expect(newAllyMcbealTonight()).toBe(true);
  });
});


var fakeDate = function(year,month,day) {
  spyOn(window, "currentDate").andCallFake(function() { return new Date(year,month,day); });
};

beforeEach(function(){
  this.addMatchers({
    toBeWithinASecondOf: function(date) {
      return Math.abs(this.actual.getTime() - date.getTime()) < 1000;
    }
  });
});