Having the exact same issue. In my TestBed config I added this to the providers. { provide: TranslateLoader, useFactory: (http: Http) => new TranslateStaticLoader(http, '/assets/i18n', '.json'), deps: [Http] } and then in my test it('should create the app', inject([TranslateService], (translate) => { let fixture = TestBed.createComponent(AppComponent); let app = fixture.debugElement.componentInstance; expect(app).toBeTruthy(); })); However, my karma test server returns a 404 for en.json. Proxies in karma conf seem to do shag all. So frustrating as I know the solution is probably very simple.