A Jasmine instruction to ease setting up asynchronous pre-conditions before, during and after tests

Since Jasmine 2.0, the runs, waits, and waitsFor methods have been removed in favor of allowing functions run as part of the spec to receive and invoke a done callback. This new approach is described at Upgrading Jasmine - Asynchronous Specs.

The done callback works great for asynchronous features with a callback (such as AJAX, jQuery animations or anything else with promises). However, there are yet other asynchronous features that will complete on their own and would be using waitsFor before Jasmine 2.0, like rendering Google Maps, images or anything else that can change both the DOM and the CSSOM.

While it is utterly possible to re-implement waitsFor I believe that Jasmine 2.0 direction is more towards stepping away from this idea and instead taking more advantage of done callbacks, like putting one it block as a pre-condition for another.

Thus, the preCondition instruction defined here will simply poll a given conditional function at a certain time interval, and once its condition is met the callback done will be fired off.

• Browser-version:
  • jasmine-precondition.js
  • jasmine-precondition.min.js
• Node.js:
  • npm install jasmine-precondition
• Karma - more on karma-jasmine-precondition
  • npm install karma-jasmine-precondition

preCondition(condition, done, interval);

where:

• condition: a conditional function that shall only return true when the condition you are expecting for is met.
• done: the done callback from beforeEach, it or afterEach must be passed here.
• interval (optional): a time interval in milliseconds between two condition executions. Default is 100.

describe('the preCondition instruction', function () {

  var counter1 = 0,
      counter2 = 0,
      interval;

  beforeEach(function(done) {
    interval = setInterval(function(){
      counter1 += 100;
    }, 100);

    preCondition(function() {
      return counter1 >= 500;
    }, done, 100);
  });

  it('should only get executed when counter1 is 500', function (done) {
    expect(counter1).toBe(500);

    preCondition(function() {
      counter2 += 200;
      return counter2 === 1000;
    }, done, 100);
  });

  it('should only get executed when counter2 is 1000', function () {
    expect(counter2).toBe(1000);
  });

  afterEach(function(){
    clearInterval(interval);
  });
});