Mocking Dependencies with Jasmine Spies

Snippet

Mocking Dependencies with Jasmine Spies

When testing Angular components, you should isolate them by mocking their dependencies. Jasmine 'spies' allow you to track calls to a function and define what it should return, preventing actual HTTP calls or side effects during tests.

snippet.js
javascript
it('should fetch data on init', () => {
  const service = TestBed.inject(DataService);
  const spy = spyOn(service, 'getData').and.returnValue(of(['Item 1']));
 
  component.ngOnInit();
 
  expect(spy).toHaveBeenCalled();
  expect(component.items).toEqual(['Item 1']);
});

angular

Breakdown

spyOn(service, 'getData')

Creates a wrapper around the service method to intercept its execution.

and.returnValue(of(['Item 1']))

Forces the spy to return a mock Observable instead of executing the original logic.

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Mocking Dependencies with Jasmine Spies

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