src/setupTests.js

import { configure } from 'enzyme';
import Adapter from 'enzyme-adapter-react-16';

configure({ adapter: new Adapter() });

class LocalStorageMock {

    constructor() {
        this.store = {};
    }

    clear() {
        this.store = {};
    }

    getItem(key) {
        return this.store[key] || null;
    }

    setItem(key, value) {
        this.store[key] = value;
    }

    removeItem(key) {
        delete this.store[key];
    }

}

global.localStorage = new LocalStorageMock();