How to Write test for login component for angular2 ( unit testing )

This is login.component.ts




    import { Component, OnInit } from '@angular/core';
    import { Router, ActivatedRoute } from '@angular/router';
    import { FormBuilder, FormGroup, Validators } from '@angular/forms';
    import { CommonModule } from  '@angular/common';


    import { LoginUser } from './loginUser.model'
    import { UserService } from './user.service';
    import { LoaderService } from '../shared/loader.service';

    import 'rxjs/add/operator/toPromise';

    @Component({
        templateUrl: './login.component.html'
    })
    export class LoginComponent implements OnInit {
        errorMessage: string;
        loginForm: FormGroup;
        loginObj = new LoginUser();

        constructor(private userService: UserService, private loaderService: LoaderService, private router: Router, fb: FormBuilder) {
            this.loginForm = fb.group({
                userName: [null, Validators.required],
                password: [null, Validators.required]
            })
            console.log(this.loginForm);
        }

    test() : void{
        console.log("This is a test");
    }
        login(loginObjValue: any): void {
            if (loginObjValue.userName == null || loginObjValue.password == null) {
                console.log('error');
            } else {
                this.loginObj.userName = loginObjValue.userName;
                this.loginObj.password = loginObjValue.password;
                this.loaderService.displayLoader(true);

                this.userService.login(this.loginObj)
                    .then((res) => {
                        console.log("data", res);
                        console.log("$localStorage.currentUser", localStorage);
                        let link = ['customercare/customer-ticket'];
                        this.loaderService.displayLoader(false);

                        this.router.navigate(link);
                    })
                    .catch(error => this.handleError(error));
            }
        }

        private handleError(error: any): Promise<any> {
            this.loaderService.displayLoader(false);

            if (error._body) {
                this.errorMessage = JSON.parse(error._body).error_description;
            }

            console.log('An error occurred', error);
            return Promise.reject(error.message || error);
        }

        ngOnInit(): void {


        }
    }





    @Component({
        templateUrl: './login.component.html'
    })
    export class LoginComponent implements OnInit {
        errorMessage: string;
        loginForm: FormGroup;
        loginObj = new LoginUser();

        constructor(private userService: UserService, private loaderService: LoaderService, private router: Router, fb: FormBuilder) {
            this.loginForm = fb.group({
                userName: [null, Validators.required],
                password: [null, Validators.required]
            })
            console.log(this.loginForm);
        }


        login(loginObjValue: any): void {
            if (loginObjValue.userName == null || loginObjValue.password == null) {
                console.log('error');
            } else {
                this.loginObj.userName = loginObjValue.userName;
                this.loginObj.password = loginObjValue.password;
                this.loaderService.displayLoader(true);

                this.userService.login(this.loginObj)
                    .then((res) => {
                        console.log("data", res);
                        console.log("$localStorage.currentUser", localStorage);
                        let link = ['customercare/customer-ticket'];
                        this.loaderService.displayLoader(false);

                        this.router.navigate(link);
                    })
                    .catch(error => this.handleError(error));
            }
        }


    }

Partial Code of userservice.ts . Please refer this code . Partial Code of userservice.ts . Please refer this code . Partial Code of userservice.ts . Please refer this code . Partial Code of userservice.ts . Please refer this code . Partial Code of userservice.ts . Please refer this code .

@Injectable()
export class UserService {
    private URL = "";

    constructor(private http: Http) { }

    login(loginObj: LoginUser) {

        let body = 'userName=' + loginObj.userName + '&password=' + loginObj.password + '&grant_type=password';

        let headers = new Headers();
        headers.append('Content-Type', 'application/x-www-form-urlencoded');

        return this.http.post(this.URL + '/token', body, { headers: headers })
            .toPromise()
            .then((res: Response) => {
                let data = res.json();
                if (data && data.access_token) {
                    localStorage.setItem('currentUser', JSON.stringify(data));
                }
                return data;
            })
    }

}

SO FAR I HAVE WRITTEN : I am unable to call login function . Please guide me .

**

    describe('LoginComponent', () => {
      let component: LoginComponent;
      let UserService:UserService;
      let fixture: ComponentFixture<LoginComponent>;

    beforeEach(async(() => {
      TestBed.configureTestingModule({
        declarations: [ LoginComponent ],
        providers: [
            { provide: UserService, useValue: UserService },
                   ]
      })

      it('should call the login method from the UserService', 
        inject([TestBed, UserService], fakeAsync((tcb: TestBed, mockUserService: UserService) => {
          spyOn(mockUserService, 'login');
    tcb
            .createComponent(LoginComponent)
            .then((fixture: ComponentFixture<LoginComponent>) => {
              tick();
               fixture.detectChanges();
              expect(mockUserService.login).toHaveBeenCalled();
            });
        }))
      );

    });

**