Test a function that contains a setTimeout()

Question

I have a close function in my component that contains a setTimeout() in order to give time for the animation to complete.

public close() {
    this.animate = "inactive"
    setTimeout(() => {
       this.show = false
    }, 250)
}

this.show is bound to an ngIf.

this.animate is bound to an animation.

I have a test that needs to test this function

it("tests the exit button click", () => {
  comp.close()
  fixture.detectChanges()
  //verifies the element is no longer in the DOM
  const popUpWindow = fixture.debugElement.query(By.css("#popup-window"))
  expect(popUpWindow).toEqual(null)
})

How do you properly test this function when there is a setTimeout()?

I was using jasmine.clock().tick(251) but the window would never disappear. any thoughts on this as well?

Solution 1

You could do one of two things:

1: Actually wait in the test 250+1 ms in a setTimeout(), then check if the element actually disappeared.

2: use fakeAsync() and tick() to simulate time in the test - a tick() will resolve the setTimeout in the original close(), and the check could happen right after in a fixture.whenStable().then(...).

For example:

it("tests the exit button click", fakeAsync(() => {
  comp.close()
  tick(500)
  fixture.detectChanges()

  fixture.whenStable().then(() => {
    const popUpWindow = fixture.debugElement.query(By.css("#popup-window"))
    expect(popUpWindow).toBe(null)
  })
}))

I suggest using the 2nd one, as it is much more faster than actually waiting for the original method. If you still use the 1st, try lowering the timeout time before the test to make the it run faster.

SEVICES

For services you do not need to call detectChanges after tick and do not need to wrap the expect statements within whenStable. you can do your logic right after tick.

  it('should reresh token after interval', fakeAsync(() => {
    // given
    const service: any = TestBed.get(CognitoService);
    const spy = spyOn(service, 'refreshToken').and.callThrough();
    ....
    // when
    service.scheduleTokenRefresh();
    tick(TOKEN_REFRESH_INTERVAL);
    // then
    expect(spy).toHaveBeenCalled();
  }));

Solution 2

In my component the method is:

hideToast() {
    setTimeout( () => {
      this.showToast = false;
    }, 5000);
  }

Test for that (explanation in comments):

it('should hide toast', () => {
  component.showToast = true; // This value should change after timeout
  jasmine.clock().install();  // First install the clock
  component.hideToast();      // Call the component method that turns the showToast value as false
  jasmine.clock().tick(5000); // waits till 5000 milliseconds
  expect(component.showToast).toBeFalsy();  // Then executes this
  jasmine.clock().uninstall(); // uninstall clock when done
});

Hope this helps!!

Solution 3

Just tried this in my project and works:

jasmine.clock().tick(10);

Solution 4

I have a method that is eerily similar to the OP's setup so thought I would add my test which I think is a lot simpler.

** Method **

public close() {
    this.animate = "inactive"
    setTimeout(() => {
       this.show = false
    }, 250)
}

** Jasmine Test **

it('should set show to "false" after 250ms when close is fired', (done) => {
      component.close();
      setTimeout(() => {
        expect(component.close).toBeFalse();
        done();
      }, 251);
    });

Note the use of 'done' to let jasmine know the test is finished and also adding 1 ms to the setTimeout to fire after my method's setTimeout.

Solution 5

this solution mentioned by @Kailas works for me:

hideToast() {
    setTimeout( () => {
      this.showToast = false;
    }, 5000);
  }

it('should hide toast', () => {
  component.showToast = true; // This value should change after timeout
  jasmine.clock().install();  // First install the clock
  component.hideToast();      // Call the component method that turns the showToast value as false
  jasmine.clock().tick(5000); // waits till 5000 milliseconds
  expect(component.showToast).toBeFalsy();  // Then executes this
  jasmine.clock().uninstall(); // uninstall clock when done
});

but sometimes you will receive this error:

Error: Jasmine Clock was unable to install over custom global timer functions. Is the clock already installed?

to resolve this issue you need to uninstall the clock first:

it('should hide toast', () => {
  jasmine.clock().uninstall()
  component.showToast = true; 
  jasmine.clock().install();  
  component.hideToast();      
  jasmine.clock().tick(5000); 
  expect(component.showToast).toBeFalsy();  
  jasmine.clock().uninstall(); 
});

View more solutions

Comments

[ed-tester]

Thank you. The second one worked, but was a little more complex then simply using tick(). I had to wrap the expects within a fixture.whenStable().then( ... //expects ). If you allow me to update your answer with this additional info I will accept it as the correct answer.

[dinvlad]

To add to that, you may need an additional fixture.detectChanges() before the tick. Then you may not need fixture.whenStable() at all (afaik fakeAsync was designed precisely to avoid such async calls).

[Sabrina Leggett]

incase it helps anyone else, the function that calls the setTimeout needs to be called within the fakeAsync method (can't be called in the beforeEach). Seems obvious but it got me!

[Jack Luo]

try jasmine.clock().tick(10);

[Nowdeen]

Thats the clean way!