How can I test the function called inside another function in Nestjs?

Question

i am writing test functions in nestjs and i am new to this task.

I mostly had problems with typeorm. but my current problem is that I do not call the paginate function in the PaginateLib class inside the function I wrote in the service. I tested the userList function directly before, but it gave paginate undefined error. Now I used mock and paginate function in test. it still gives undefined error.

Here's my admin.service code

  public async userList(page, limit): Promise<any> {
    const opt = {
      relations: ['userInfo'],
    };
    const userData = await this.paginateLib.paginate(
      getRepository(Users),
      opt,
      page,
      limit,
    );
    return userData;
  }

Here's Paginate function code in PaginateLib class. I'm cutting this short as I don't think it's very necessary.

export class PaginateLib {
  async paginate(repo, opt, page, limit) {
    try {
      page = Number(page);
      limit = Number(limit);
      const items = (Number(page) - 1) * Number(limit);

      const [data, count] = await repo.findAndCount({
        ...opt,
        skip: Number(items),
        take: Number(limit),
      });
      if (count <= items) {
        return [];
      }

and here's my test code

class PaginateMock {
  paginate(repo: any, opt: any, page: number, limit: number) {
    return [];
  }
}

describe('AdminService', () => {
  let service: AdminService;
  let connection: Connection;
  let module: TestingModule;
  let services: PaginateLib;

  beforeAll(async () => {
    const ApiServiceProvider = {
        provide: PaginateLib,
        useClass: PaginateMock,
      },
      module = await Test.createTestingModule({
        imports: [
          TypeOrmModule.forRoot({
            type: '****',
            host: '****',
            port: ****,
            username: '****',
            password: '****',
            database: '****',
            entities: [__dirname + '/../../**/*.entity.ts'],
            synchronize: true,
          }),
        ],
        providers: [
          AdminService,
          ApiServiceProvider,
        ],
      }).compile();

    service = module.get<AdminService>(AdminService);
    services = module.get<PaginateLib>(PaginateLib);
  });

  // afterAll(async () => {
  //   await module.close();
  // });

  describe('User Info', () => {
    it('should be get user list', async () => {   
      const paginateSpy = jest.spyOn(services, 'paginate');
      expect(paginateSpy).toHaveBeenCalled();
      expect(true).toBe(service.userList(1, 1));
    });
});
});

I tried different things many times. but the error I get is undefined. what should I do? Is there anyone have an idea?thank you

Answer 1

Try this:

describe('User Info', () => {
    it('should be get user list', async () => {   
      const paginateSpy = jest.spyOn(services, 'paginate');
      const userData = await service.userList(1, 1);
      expect(paginateSpy).toHaveBeenCalled();
      expect(userData).toBe(); // Don't know what userData actually looks like. So this is up to you
    });
});