How to test asynchronous function in Jasmine?

[aditya jain]

Hi, I am using an asynchronous function in a class, which is below:

home.ts

//I am displaying only the function definition in the class I have used.

  click(){


   function delayedAlert(message, time,cb){


              return setTimeout( ()=> cb(message), time);
           }


//function calling


delayedAlert('xyz', 3000, (message)=> console.log(message));
     
        }

In the spec.ts file I write the test code for the above function using TestBed.How to write the test using done ?

spec.ts

describe('Asynchronous call', () => {

let fixture: ComponentFixture<HomePage>;

let comp: HomePage;

let de: DebugElement;

let el: HTMLElement;

let message: string;

beforeEach(async(() => {

TestBed.configureTestingModule({

declarations: [HomePage],

imports: [

IonicModule.forRoot(HomePage),

],

providers: [NavController],

}).compileComponents();

}));

beforeEach(() => {

fixture = TestBed.createComponent(HomePage);

comp = fixture.componentInstance;

de = fixture.debugElement;

});

it('test', function (done) {

//how to write the test using (done)??

})

})

[Gregg Van Hove]

There are two main ways that Jasmine gives you to test code that is asynchronous in nature.

1. Using the mock clock (https://jasmine.github.io/api/edge/Clock.html) (https://jasmine.github.io/edge/introduction#section-Jasmine_Clock)

2. Using the `done` callback (or Promises and `async` functions after 2.7)

Given your example code, I would recommend using the mock clock, which will let you manually `tick` to move the time forward in your test and have your callback be called without actually having to wait for 3 seconds during the test.

For an asynchronous function that is mostly about the side-effects it causes, in order to have your spec be truly async, you'd need to have it sort of wake up and check if the callback had been called yet, only calling `done` once that had successfully happened.

Hope this helps. Thanks for using Jasmine!

-Gregg

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