function createHeroSidekickSelector$(heroId: number): Observable<Sidekick> {
   const { selectHeroMap, selectSidekickMap } = setCollectionSelectors();
   const selectHero = createSelector(selectHeroMap, heroes => heroes[heroId]);
   const selectSideKick = createSelector(selectHero, selectSidekickMap, (hero, sidekicks) => {
     const sidekickId = hero && hero.sidekickFk;
     return sidekicks[sidekickId];
   });
   return store.select(selectSideKick);
 }

    it('should recursively release ancestor selectors', () => {
      const grandparent = createSelector([incrementOne], a => a);
      const parent = createSelector([grandparent], a => a);
      const child = createSelector([parent], a => a);
      spyOn(grandparent, 'release').and.callThrough();
      spyOn(parent, 'release').and.callThrough();

      child.release();

      expect(grandparent.release).toHaveBeenCalled();
      expect(parent.release).toHaveBeenCalled();
    });

  function getSelectors(
    selectState?: (state: any) => EntityState<T>
  ): EntitySelectors<T, any> {
    const selectIds = (state: any) => state.ids;
    const selectEntities = (state: EntityState<T>) => state.entities;
    const selectAll = createSelector(
      selectIds,
      selectEntities,
      (ids: T[], entities: Dictionary<T>): any =>
        ids.map((id: any) => (entities as any)[id])
    );

    const selectTotal = createSelector(selectIds, ids => ids.length);

    if (!selectState) {
      return {
        selectIds,
        selectEntities,
        selectAll,
        selectTotal,
      };
    }

    return {
      selectIds: createSelector(selectState, selectIds),
      selectEntities: createSelector(selectState, selectEntities),
      selectAll: createSelector(selectState, selectAll),
      selectTotal: createSelector(selectState, selectTotal),
    };
  }