Angular 10 - Guard unit test

I need an advice how to test Guards with some logic like, because I am a little bit confused, how to use mocks/spies in Jasmine/Karma:

@Injectable({
    providedIn: 'root'
})
export class RegistrationGuardService implements CanActivate {

    constructor(private credentials: CredentialsService,
                private router: Router) {
    }

    canActivate(route: ActivatedRouteSnapshot, routerState: RouterStateSnapshot): Observable<boolean | UrlTree> | Promise<boolean | UrlTree> | boolean | UrlTree {
        return this.credentials.getAuthorities().then(() => {
            if (!this.credentials.isGuestOrAdmin()) {
                this.router.navigate(['/sign-in'], {state: {url: routerState.url}});
            }
            return this.credentials.isGuestOrAdmin();
        });
    }
}

and this is service:

export class CredentialsService {
    authenticated: boolean = false;
    authorities: UserRole[];

    constructor(private router: Router,
                private authenticationService: AuthenticationService,
                private authorizationService: AuthorizationService,
                private notificationService: NotificationService) {
        this.getAuthorities().then();
    }

    public async getAuthorities() {
        await this.authorizationService.getAuthorities()
            .pipe(
                map(authorities => authorities.map(element => UserRole.getUserRoleType(element)))
            )
            .toPromise()
            .then(result => {
                this.authorities = result;
                this.authenticated = this.isNotAnonymous();
            })
            .catch(() => {
                this.authorities = [UserRole.ANONYMOUS];
                this.authenticated = this.isNotAnonymous();
            })
    }
}

Is it any possibility to mock services? I tried many things with using TestBed.inject() but without success.

Version of software:

• Angular 10.1.0,
• Jasmine Core 3.6.0,
• Karma 5.2.1