Counter app store example - TypeScript + React + Redux + typescript-fsa: : https://gist.github.com/kotarella1110/3c42138ba0d53d1eba0cecd6fee23dbc

counter.test.ts

import { actions, reducer } from './counter';

describe('counter actions', () => {
  it('increment should create counter/INCREMENT action', () => {
    expect(actions.increment()).toEqual({
      type: 'counter/INCREMENT',
    });
  });

  it('decrement should create counter/DECREMENT action', () => {
    expect(actions.decrement()).toEqual({
      type: 'counter/DECREMENT',
    });
  });
});

describe('counter reducer', () => {
  it('should handle counter/INCREMENT', () => {
    expect(reducer(0, actions.increment())).toEqual(1);
  });

  it('should handle counter/DECREMENT', () => {
    expect(reducer(1, actions.decrement())).toEqual(0);
  });
});

counter.ts

import actionCreatorFactory from 'typescript-fsa';
import { reducerWithInitialState } from 'typescript-fsa-reducers';

export type Action =
  | ReturnType<typeof increment>
  | ReturnType<typeof decrement>;

const actionCreator = actionCreatorFactory('counter');

const increment = actionCreator('INCREMENT');
const decrement = actionCreator('DECREMENT');

export const actions = { increment, decrement };

export interface State {
  readonly counter: number;
}

const initialState = 0;

export const reducer = reducerWithInitialState(initialState)
  .case(increment, state => state + 1)
  .case(decrement, state => state - 1);