actions.ts

export const fetchUser = createAsyncThunk<Cleaner>(
  "authentication/fetchUser",
  async () => {
    const cleaner = await authenticationApi.fetchUser();
    return cleaner;
  }
);

selectors.ts

export const getAuthenticationToken = (state: AppState) =>
  state.authentication.token;

export const isAuthenticated = createSelector(
  getAuthenticationToken,
  token => token !== null
);

export const isPending = (state: AppState) => state.authentication.pending;

export const getCurrentUser = (state: AppState) => state.authentication.user;

test.ts

it(`handles .fetchUser`, async () => {
  // Given
  const store = configureStore({ reducer });

  jest
    .spyOn(authenticationApi, "fetchUser")
    .mockReturnValue(Promise.resolve(cleaner));

  // When
  await store.dispatch(fetchUser());
  
  // Then
  expect(isPending(store.getState()).toBe(true);
         
  // When the fetching is completed
  await wait(() => expect(isPending(store.getState()).toBe(false));

  // Then
  expect(getCurrentUser(store.getState())).toBe(cleaner);
});

it(`handles .logout`, async () => {
  // Given
  const store = configureStore({
    reducer,
    preloadedState: {
      authentication: {
        token: "asdf",
        user: cleaner
      }
    }
  });

  // When
  await store.dispatch(logout());
  const state = store.getState();

  // Then
  expect(getAuthenticationToken(state)).toEqual(null);
  expect(getCurrentUser(state)).toEqual(null);
  expect(isAuthenticated(state)).toBe(false);
});