我有一个@ionic/storage-angular的StorageService Package 器，其中有一个函数，大致如下所示：

import { Injectable } from '@angular/core';
import { Storage } from '@ionic/storage-angular';

@Injectable({
  providedIn: 'root'
})
export class StorageService {
  constructor(public storage: Storage) {}

  async getData() {
    const data = [];
    await this.initStorage();

    return new Promise((resolve) => {
      this.storage
        .forEach((value, key) => {
          if (key.startsWith('data-')) {
            data.push({
              key: 'someKey,
              value,
            });
          }
        })
        .then(() => resolve(data));
    });
  }

  // other functions here
}

我有一个单元测试，如下所示

import { CUSTOM_ELEMENTS_SCHEMA } from '@angular/core';
import { fakeAsync, flush, TestBed } from '@angular/core/testing';
import { StorageService } from './storage.service';
import { Storage } from '@ionic/storage-angular';

describe('StorageService', () => {
  let service: StorageService;
  let mockStorage: jasmine.SpyObj<Storage>;

  beforeEach(() => {
    mockStorage = jasmine.createSpyObj('Storage', ['get', 'set', 'remove', 'create']);

    TestBed.configureTestingModule({
      schemas: [CUSTOM_ELEMENTS_SCHEMA],
      providers: [
        { provide: Storage, useValue: mockStorage },
      ],
    });
    service = TestBed.inject(StorageService);
  });

  describe('getData()', () => {
    it('should call StorageService.initStorage()', fakeAsync(() => {
      spyOn<any>(service, 'initStorage').and.stub();

      service.getData();
      flush();

      expect(service['initStorage']).toHaveBeenCalled();
    }));
  });

  // other tests here
});

它失败于

Error: Uncaught (in promise): TypeError: _this.storage.forEach is not a function
        TypeError: _this.storage.forEach is not a function

存储本身应该是可迭代的，但jasmine并不这么认为，我想是因为我嘲笑它的方式。
问题是：如何正确地对这一位进行单元测试？我不想为测试目的创建一个真实的存储示例，有没有办法通过模拟将www.example.com定义为可迭代的？this.storage as iterable via mocks?