Angular 单元测试错误：无法从同步测试中调用 Promise.then

我开始研究单元测试Angular 为2的应用程序，但即使是最简单的示例我也被困住了.我只想运行一个简单的测试，看看它是否正常工作，基本上我想要的是将标题页中的值与测试中的值进行比较.

这就是我收到的错误，但我看不出错误来自哪里，因为对我来说一切看起来都是同步的.

错误:错误:无法调用promise .然后在同步测试中.

单元测试:

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { By }              from '@angular/platform-browser';
import { DebugElement, Input}    from '@angular/core';
import { ToDoComponent } from './todo.component';
import { FormsModule } from '@angular/forms';
describe(("test input "),() => {
    let comp:    ToDoComponent;
    let fixture: ComponentFixture<ToDoComponent>;
    let de:      DebugElement;
    let el:      HTMLElement;

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

    fixture = TestBed.createComponent(ToDoComponent);
    comp = fixture.componentInstance;
    de = fixture.debugElement.query(By.css("h1"));
    el = de.nativeElement;

    it('should display a different test title', () => {
        comp.pageTitle = 'Test Title';
        fixture.detectChanges();
        expect(el.textContent).toBe('Test Title423');
    });
});

我的组件:

import {Component} from "@angular/core";
import {Note} from "app/note";

@Component({
    selector : "toDoArea",
    templateUrl : "todo.component.html"
})

export class ToDoComponent{
    pageTitle : string = "Test";
    noteText : string ="";
    noteArray : Note[] = [];
    counter : number = 1;
    removeCount : number = 1;

    addNote() : void {

        if (this.noteText.length > 0){
            var a = this.noteText;
            var n1 : Note = new Note();
            n1.noteText = a;
            n1.noteId = this.counter;
            this.counter = this.counter + 1;
            this.noteText = "";
            this.noteArray.push(n1);        
        }

    }

    removeNote(selectedNote : Note) :void{
        this.noteArray.splice(this.noteArray.indexOf(selectedNote),this.removeCount);
    }

}