Err: Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL

people! Please, be kind to share your ideas about fixing the following. While writing a test for Angular2 component I encountered this kind of error:

Error: Timeout - Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL.

The component under test is: (sorry, it is bulky)

The test:

import { TestBed, ComponentFixture, async, inject } from '@angular/core/testing';
import { DebugElement } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import {Injectable} from '@angular/core';

import {FormGroup, FormBuilder, ReactiveFormsModule} from '@angular/forms';

import {Observable} from 'rxjs/Observable';
import 'rxjs/add/observable/of';

import SignupComponent from './signup.component';
import {UserService} from '../services/user.service';


@Injectable()
export class MockUserService {
    public signup(user: any) {
        return Observable.of({});
    }
}

let component: SignupComponent;
let fixture: ComponentFixture<SignupComponent>;

describe('SignupComponent', () => {
     beforeEach(async(() => {
         TestBed.configureTestingModule({
            declarations: [ SignupComponent ],
            imports: [
                 BrowserModule,
                 ReactiveFormsModule
            ]
        })
        .overrideComponent(SignupComponent, {
            set: {
                templateUrl: 'app/components/signup.component.html'
            }}
        )
        .overrideComponent(SignupComponent, {
            set: {
                providers: [
                    { provide: UserService, useClass: MockUserService },
                ]
            }
        })
        .compileComponents().then(createComponent);
}));

    it('should create an instance', () => {
        expect(component).toBeDefined();
    });
});

 /***** HELPERS *****/
 function createComponent() {
      fixture = TestBed.createComponent(SignupComponent);
      component = fixture.componentInstance;
      fixture.detectChanges();

     return fixture.whenStable().then(() => {
         fixture.detectChanges();
     });
 }