Testing error case with observables in services

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You can simply mock Observable throw error object like Observable.throw({status: 404})and test error block of observable.

const xService = fixture.debugElement.injector.get(SomeService);
const mockCall = spyOn(xService, 'method').and.returnValue(Observable.throw({status: 404}));

Update 2019 :

Since some people are lazy to read comment let me put this here :
It’s a best practice to use errors for Rxjs

import { throwError } from 'rxjs'; // make sure to import the throwError from rxjs
const xService = fixture.debugElement.injector.get(SomeService);
const mockCall = spyOn(xService,'method').and.returnValue(throwError({status: 404}));

Update 2022:
Use of throwError in the aforementioned way is deprecated. Instead, use throwError(() => new Error({status: 404})):

import { throwError } from 'rxjs'; // make sure to import the throwError from rxjs
const xService = fixture.debugElement.injector.get(SomeService);
const mockCall = spyOn(xService,'method').and.returnValue(throwError(() => new Error({status: 404})));

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