ElementRef : Karma给出错误: NullInjectorError:没有Angular提供程序！从v7升级到v8之后

import { Component, ElementRef } from '@angular/core';

@Component({
  selector: 'app-example',
  template: '<div></div>'
})
export class ExampleComponent {
  constructor(private elementRef: ElementRef) {
    // 在构造函数中注入ElementRef
  }
}

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { ExampleComponent } from './example.component';
import { ElementRef } from '@angular/core';

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

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [ ExampleComponent ],
      providers: [ ElementRef ] // 提供ElementRef
    })
    .compileComponents();
  });

  beforeEach(() => {
    fixture = TestBed.createComponent(ExampleComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});