Is it possible to use ts-jest / jest to spy on a generic function and mock a return value in Typescript environment?

Question

I am new user trying to learn jest in a Typescript environment via ts-jest. One of the functions that I wish to 'spyOn' uses generics. Is it possible to spy on a generic function and mock a typed return value?

For example:

export class Api {
  private api: AxiosInstance;

  constructor(api: AxiosInstance = axios) {
    this.api = api;
  }

  public all<T, From = T, TF extends ITransform<From, T> = never>(
    url: string,
    transformer?: TF,
  ): Observable<AxiosResponse<T[]>> {
    return this.requestAll<T, From, TF>(url, transformer);
  }

I have tried with:

const allSpy = jest.spyOn<Api, 'all'>(Api.prototype, 'all');

In this case allSpy has the following type information:

const allSpy: jest.SpyInstance<Observable<AxiosResponse<unknown[]>>, [string, (ITransform<any, any> | undefined)?]>

I receive a type compilation error if I try to mock a return value:

 const response: AxiosResponse<MyObj[]> = {
      data: [
        { id: 1014760, objName: 'Object 1' },
        { id: 1015762, objName: 'Object 2' },
      ],
      status: 200,
      statusText: 'ok',
      headers: {},
      config: {},
    };
allSpy.mockReturnValueOnce(response); // type error for response

Answer 1

尝试存根而不是间谍，你将能够得到它。