问如何将外部库包含到单元测试中：：Angular2-CLI

EN

Error: Error in :0:0 caused by: Plotly is
ReferenceError: Plotly is not defined

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { By } from '@angular/platform-browser';
import { DebugElement } from '@angular/core';
import { FormsModule } from '@angular/forms';
import { MaterialModule } from '@angular/material';
import { WatchlistComponent } from './watchlist.component';
declare let Plotly: any;

describe('SystemComponent', () => {
  let component: WatchlistComponent;
  let fixture: ComponentFixture<WatchlistComponent>;
  let element;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ WatchlistComponent ],
      imports: [ FormsModule, MaterialModule ]
    })
    .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(WatchlistComponent);
    component = fixture.componentInstance;
    element = fixture.nativeElement;
    fixture.detectChanges();
  });


  it('should return a positive number', () => {
    expect(component.getScreenHeight()).toMatch(/\d+/);
  });

});