custom elements schema error occur while unit testing with jasmine and karma

1import { TestBed, async } from '@angular/core/testing';
2import { AppComponent } from './../app.component';
3import { RouterTestingModule } from '@angular/router/testing';
4import { CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';
5
6describe('AppComponent', () => {
7  beforeEach(() => {
8    TestBed.configureTestingModule({
9      schemas: [ CUSTOM_ELEMENTS_SCHEMA ],
10      declarations: [AppComponent],
11      imports: [RouterTestingModule]
12    });
13    TestBed.compileComponents();
14  });
15