F_A_8_Test_app/src/reducers/index.js

// Сюда добавляем редьюсеров для combineReducers и импортируем их в state,
// для создания store 
import { combineReducers } from 'redux';

import user from './user';
import cards from './cards';
import { reducer as form } from 'redux-form';

const combinedReducers = combineReducers({
    form,
    user,
    cards
})

export default combinedReducers;