Exploring Angular2 components featuring setInterval or setTimeout functions

I have a basic ng2 component that interacts with a service to retrieve carousel items and automatically cycle through them using setInterval. Everything functions properly, but I encounter the error "Cannot use setInterval from within an async test zone" when running Jasmine tests.

Even after attempting to wrap the setInterval call in this.zone.runOutsideAngular(() => {...}), the error persists. Switching the test to run in fakeAsync zone leads to another error stating XHR calls are not allowed within fakeAsync test zone (which is understandable).

How can I integrate both XHR calls and the interval in my tests without encountering these issues? My project is based on ng2 rc4 and was generated by angular-cli. Thank you for any help in advance.

The code snippet from the component is shown below:

constructor(private carouselService: CarouselService) {
}

ngOnInit() {
    this.carouselService.getItems().subscribe(items => { 
        this.items = items; 
    });
    this.interval = setInterval(() => { 
        this.forward();
    }, this.intervalMs);
}

And here is the relevant part of the Jasmine spec:

it('should display carousel items', async(() => {
    testComponentBuilder
        .overrideProviders(CarouselComponent, [provide(CarouselService, { useClass: CarouselServiceMock })])
        .createAsync(CarouselComponent).then((fixture: ComponentFixture<CarouselComponent>) => {
            fixture.detectChanges();
            let compiled = fixture.debugElement.nativeElement;
            // add your expectations here;
    });
}));

Answer №1

Writing clean code is essential for maintainability and testability. One common challenge in testing code that involves timing, like using setInterval, is achieving perfect timing in tests. To address this issue, it's recommended to abstract the setTimeout functionality into a separate service that can be easily mocked during testing. By doing so, you can have better control over the timing of intervals in your tests.

class IntervalService {
  interval;

  setInterval(time: number, callback: () => void) {
    this.interval = setInterval(callback, time);
  }

  clearInterval() {
    clearInterval(this.interval);
  }
}

class MockIntervalService {
  callback;

  clearInterval = jasmine.createSpy('clearInterval');

  setInterval(time: number, callback: () => void): any {
    this.callback = callback;
    return null;
  }

  tick() {
    this.callback();
  }
}

The MockIntervalService provides an easy way to simulate each interval tick during testing, making it more straightforward to reason about. Additionally, there's a spy to verify that the clearInterval method is invoked correctly when the component is destroyed.

If you're working with asynchronous operations in a service like CarouselService, check out this post for a helpful solution.

Below is a complete example (using RC 6) showcasing how these services can be utilized:

// Code example omitted for brevity

Answer №2

Encountering a similar issue, I faced an error message when a third-party service invoked setInterval() during a test:

Error: The utilization of setInterval within an async zone test is not permitted.

While it's possible to simulate the calls, this may not always be the preferred approach as you might intend to assess the interaction with another module.

In my scenario, the problem was resolved by opting for Jasmine's (version>=2.0) asynchronous support rather than Angular's async():

it('Testing MyAsyncService', (done) => {
  const myService = new MyAsyncService();
  myService.find().timeout(1000).toPromise() // find() returns Observable.
    .then((m) => { console.warn(m); done(); })
    .catch((e) => { console.warn('An error occurred: ' + e); done(); })
  console.warn("End of the test.")
});

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