Unit test Redux Toolkit using React Testing Library guideline

Can somebody learn me please how to unit test redux toolkit using react testing library? I tried to do like in the redux toolkit documentation, but no result. Also I've tried all solutions found, but maybe I'm doing something wrong.

my.service.ts

export const allHeadcountApiPaths = {
  fetchAllHeadcount: (params: IQueryParams) =>
    `${ApiUrlService.getTDS()}/rpc/v1/version/${params.versionId}/planned-headcount/view/with-relations${buildQuery(params)}`,
};

export const fetchBeginningHeadcount = createAsyncThunk('allHeadcount/fetchBeginningHeadcount', async (params: IQueryParams) => {
  const response = await api('GET', allHeadcountApiPaths.fetchAllHeadcount(params), {});
  return response.data;
});

my.slice.ts

export const initialState = new AllHeadcountState()

const allHeadcountSlice = createSlice({
  name: 'allHeadcount',
  initialState,
  reducers: {},
  extraReducers: builder => {
    builder
      .addCase(fetchBeginningHeadcount.pending, state => {
        return requestListData<IAllHeadcountState, IHeadcount[]>({ ...state }, ['beginningHeadcount'])
      })
      .addCase(fetchBeginningHeadcount.fulfilled, (state, action) => {
        const { content, totalElements, totalPages } = action.payload
        return receiveListData<IAllHeadcountState, IHeadcount[]>({ ...state }, ['beginningHeadcount'], content, totalElements, totalPages)
      })
      .addCase(fetchBeginningHeadcount.rejected, (state, action) => {
        return errorListData<IAllHeadcountState, IHeadcount[]>({ ...state }, ['beginningHeadcount'], String(action.error.message))
      })
   },
})

export default allHeadcountSlice.reducer

my.provider.ts

   const render = (ui: ReactElement, { initialState = {}, initializedStore = store, ...renderOptions } = {}): RenderResult => {
  const Wrapper = ({ children }: PropsWithChildren): JSX.Element => {
    return <Provider store={initializedStore}>{children}</Provider>
  }
  return rtlRender(ui, { wrapper: Wrapper, ...renderOptions })
}

export * from '@testing-library/react'
export { render }

Also, I don't understand, should be written tests separately for service and slice, or one test covers them both?! Please help me to understand how these tests should work! Thanks in advance!