Testable Redux Reducer

testableReducer.ts

import {
  PayloadAction,
  createReducer,
} from "@reduxjs/toolkit";
import { increment, decrement, incrementByAmount, incrementAsync } from "./actions";

export interface CounterState {
  value: number;
  status: "idle" | "loading" | "failed";
}

const initialState: CounterState = {
  value: 0,
  status: "idle",
};


export const testableCounterReducer = createReducer(initialState, (builder) =>
  builder
    .addCase(increment, (state) => ({ ...state, value: state.value + 1 }))
    .addCase(decrement, (state) => ({ ...state, value: state.value - 1 }))
    .addCase(incrementByAmount, (state, action: PayloadAction<number>) => ({
      ...state,
      value: state.value + action.payload,
    }))
    .addCase(incrementAsync.pending, (state) => ({
      ...state,
      status: "loading",
    }))
    .addCase(incrementAsync.fulfilled, (state, action) => ({
      ...state,
      status: "idle",
      value: state.value + action.payload,
    }))
);