如何测试angular服务中的变量

import { TestBed } from '@angular/core/testing';
import { YourService } from './your.service';

describe('YourService', () => {
  let service: YourService;

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

  it('should have initial value', () => {
    expect(service.variable).toBeDefined();
    expect(service.variable).toEqual('initial value');
  });

  it('should update variable', () => {
    service.updateVariable('new value');
    expect(service.variable).toEqual('new value');
  });

  it('should handle edge cases', () => {
    service.updateVariable('');
    expect(service.variable).toEqual('');
    
    service.updateVariable(null);
    expect(service.variable).toEqual(null);
    
    service.updateVariable(undefined);
    expect(service.variable).toEqual(undefined);
  });
});