I want to test my service in angular with karma and jasmine, I begin with unit tests and I don't found any solution for my case or because I don't know how I can fix the issue. I always have a problem with my fields which are often undefined I don't understand why. If you can explain me what is the real problem It will be very nice to be able to progress in my tests.

My service

import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class CanvasElementService {

  public canvasContainer: HTMLDivElement;

  private scaleProperty: string = 'scale(1)';

  public updateScale(scale: number) {
    this.scaleProperty = `scale(${scale})`;
    this.update();
  }

  public update(): void {
    this.canvasContainer.style.transform = this.scaleProperty;
  }

}

And my test

import { Component } from '@angular/core';
import { TestBed } from '@angular/core/testing';

import { CanvasElementService } from './canvas-element.service';


fdescribe('CanvasElementService', () => {
  let service: CanvasElementService;


  beforeEach(() => {
    TestBed.configureTestingModule({});
    service = TestBed.inject(CanvasElementService);
  });

  it('should be created', () => {
    expect(service).toBeTruthy();
  });

  describe("updateScale", () => {
    it("updatescale 2", () => {
      let scale = 3;
      spyOn(service, 'update').and.callThrough();
      service.updateScale(scale);
      expect(service['scaleProperty']).toBe('scale(3)');
    });


  });

});

After run test I got :

thanks for help If you have any idea to fix it.