Testing a callback function within a method in Angular

Question

Testing a callback function within a method in Angular

I am currently working with Angular 11 using TypeScript and I am unsure how to properly test scenarios where an exception is raised within my method.

myMethod() {
    this.myService.callBackend(id).subscribe(() => {
       // do something when success
    }, responseKo => {
      if (responseKo instanceof HttpErrorResponse) {
        if (responseKo.status === 400) {
          // do something when we have bad request
        } else {
          throw responseKo;
        }
      } else {
        throw responseKo;
      }
    });
}

For testing, I am utilizing the jasmine and karma frameworks. How can I effectively test the scenario in which an exception is thrown?

angular typescript jasmine karma-jasmine

Answer 1

Answer №1

When implementing observables, the focus was on handling asynchronicity effectively. Therefore, your tests will need to be made asynchronous with the use of fakeAsync. In fakeAsync tests, the tick function allows you to "flush out" any asynchronous events. In your scenario, you can take advantage of this by expecting tick to throw an error:

 it('should throw', fakeAsync(() => {
    of(true).subscribe(() => {
        throw new Error('something thrown');
    });
    expect(tick).toThrow();
  }));

Answer 2

When implementing observables, the focus was on handling asynchronicity effectively. Therefore, your tests will need to be made asynchronous with the use of fakeAsync. In fakeAsync tests, the tick function allows you to "flush out" any asynchronous events. In your scenario, you can take advantage of this by expecting tick to throw an error:

 it('should throw', fakeAsync(() => {
    of(true).subscribe(() => {
        throw new Error('something thrown');
    });
    expect(tick).toThrow();
  }));

Answer 3

Answer №2

It seems that in your testing setup, you may be using spy methods to mimic behavior. If you want to test how your code handles errors, you can simulate an error situation by returning an error observable from your method. You can achieve this by using the throwError function to create an observable.

it('should handle errors gracefully', () => {
  serviceMock.callBackend.and.returnValue(throwError(myErrorObject));
  myComponent.myMethod();
});

Answer 4

It seems that in your testing setup, you may be using spy methods to mimic behavior. If you want to test how your code handles errors, you can simulate an error situation by returning an error observable from your method. You can achieve this by using the throwError function to create an observable.

it('should handle errors gracefully', () => {
  serviceMock.callBackend.and.returnValue(throwError(myErrorObject));
  myComponent.myMethod();
});

Testing a callback function within a method in Angular

Answer №1

Answer №2

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