如何模拟一个angular服务来为不同的测试返回不同的结果？

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

@Injectable()
export class MockDataService {
  getData() {
    // 返回默认的测试数据
    return 'Default data';
  }

  getTestData() {
    // 返回测试用的数据
    return 'Test data';
  }
}

import { TestBed } from '@angular/core/testing';
import { MyComponent } from './my.component';
import { MockDataService } from './mock-data.service';

describe('MyComponent', () => {
  let component: MyComponent;
  let mockDataService: MockDataService;

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [
        { provide: MockDataService, useClass: MockDataService }
      ]
    });

    component = TestBed.createComponent(MyComponent).componentInstance;
    mockDataService = TestBed.inject(MockDataService);
  });

  it('should use default data if no test data is provided', () => {
    spyOn(mockDataService, 'getData').and.returnValue('Mocked data');

    // 在这里进行测试逻辑
    // ...

    expect(component.data).toBe('Mocked data');
  });

  it('should use test data if provided', () => {
    spyOn(mockDataService, 'getTestData').and.returnValue('Test data');

    // 在这里进行测试逻辑
    // ...

    expect(component.data).toBe('Test data');
  });
});