Reactnative reduxobservable Promise 在单元测试中没有得到解决

我正在测试这部史诗https://github.com/zarcode/unsplashapp/blob/master/src/epics/photos.js.问题是当我运行测试时map永远不会发生(我假设这意味着promise 永远不会解决)，所以photosSuccess操作也永远不会发生:

export const loadPhotosToList = (action$: Observable<Action>, state$: 
Object): Observable<Action> => {
  const state = (photosFilter: PhotosFilter) => state$.value.photos[photosFilter];
  return action$
  // .ofType(ACTION.FETCH_PHOTOS_REQUESTED)
    .pipe(
      filter((a: Action) =>
        a.type === ACTION.FETCH_PHOTOS_REQUESTED &&
        ((state(a.filter).loadingState === 'idle' && !state(a.filter).isLastPage) || a.refresh)),
      switchMap((a) => {
        const nextPage = !a.refresh ? state(a.filter).lastLoadedPage + 1 : 1;
        const loadingAction = of(photosActions.photosLoading(a.filter, a.refresh));
        const request = api.fetchPhotos({
          page: nextPage,
          per_page: perPage,
          order_by: a.filter,
        });
        const requestAction = from(request)
          .pipe(
            // tap(data => { console.log("data", data); }),
            map(data =>
              photosActions.photosSuccess(
                data,
                a.filter,
                nextPage,
                data.length < perPage,
                a.refresh,
              )),
            catchError(e => of(photosActions.photosFail(e.message, a.filter))),
          );
        // requestAction.subscribe(x => console.log("-------",x));
        return loadingAction
          .pipe(
            concat(requestAction),
            takeUntil(action$
              .pipe(filter(futureAction => futureAction.type === ACTION.FETCH_PHOTOS_REQUESTED))),
          );
      }),
    );
};

然而，如果我做了requestAction.subscribe个promise ，我就会得到解决，并在控制台日志(log)中得到结果.

Note:只有当我运行这个测试时才会发生这种情况https://github.com/zarcode/unsplashapp/blob/master/src/epics/photos.test.js，应用程序代码工作正常，数据获取正常.

问题是:如何正确编写这个测试？