嘗試在我的 angular 8 應用程序中執行單元測試時，我收到 TypeError: cannot read property 'id' of undefined 。這是我的模板<h4>{{student.id}}</h4>這是我的組件import {Component, EventEmitter, Input, OnInit} from '@angular/core';import { Student } from '@app/app-types';@Component({...... saved some typing})export class StudentComponent implements OnInit {@Input() student: Student;refreshForm: EventEmitter<any>;constructor(){}ngOnInit(){  this.refreshForm = new EventEmitter();  }}這是單元測試import {async, ComponentFixture, TestBed } from '@angular/core/testing';import {StudentComponet} from './student-component';describe('StudentComponet', () => {  let component: StudentComponent;  let fixture: ComponentFixture<StudentComponent>;    beforeEach(async(() => {  TestBed.configureTestingModule({    declarations: [StudentComponent]  }).compileComponents();  }));    beforeEach(() => {    fixture = TestBed.createComponent(StudentComponent);    component = fixture.componentInstance;    fixture.detectChanges();  });    it('should create', () => {  expect(component).toBeTruthy();  })    });