angular2 testing using jasmine for subscribe method - unit-testing

Question

I have a spec code to test like this
it('login test', () => {
const fixture = TestBed.createComponent(component);
fixture.detectChanges();
let authService = fixture.debugElement.injector.get(Auth);
spyOn(authService, 'login').and.returnValue('');
const elements = fixture.nativeElement;
fixture.componentInstance.login();
expect(authService.login).toHaveBeenCalled();
});
and the implementation code like this
login() {
this.auth.login(this.username, this.password).subscribe(() => {
}
});
}
it gives error:
this.auth.login(...).subscribe is not a function
Why does this error happen?

Answer 1

You need to return something with a subscribe method, as the component calls subscribe directly from login. A string does not. You could just return an object with a subscribe function and it should work
and.returnValue({ subscribe: () => {} });
Or if you want to pass a real observable, you could
and.returnValue(Observable.of('some value'));
You might need to import rxjs/add/observable/of

Answer 2

On rxjs v6 you should use of instead of Observable.of or Observable.from e.g
const loginService: any = {
getUser: () => of(['Adam West']),
};
and import
import { of } from 'rxjs';

Answer 3

Change your spy for the 'login' method on your authService to return an observable instead of a value. You'll need to import:
import 'rxjs/add/observable/from';
import {Observable} from 'rxjs/Observable';
Setup your spy:
const loginResult = '';
const spy = spyOn(authService, 'login').and.callFake(() => {
return Observable.from([loginResult]);
})
Call login:
fixture.componentInstance.login();
Assert:
expect(spy).toHaveBeenCalled();