diligent-react-native/store/reducers/test.js

import { createReducer } from '@reduxjs/toolkit'
import { increment, decrement } from '../actions/index'

export default createReducer({
  value: 0
}, builder => {
  builder
    .addCase(increment, (state) => {
      state.value += 1
    })
    .addCase(decrement, (state) => {
      state.value -= 1
    })
})