a unit testable document.cookie mock

fakeDocumentCookie.js

// idea  from here @see https://stackoverflow.com/questions/6456429/is-it-possible-to-mock-document-cookie-in-javascript
const fakeDocumentCookie = {
  cookies: '',
  
  get cookie() {
    return this.cookies;
  },
  
  set cookie(cookieValue) {
    const cookies = this.cookies.split(' ');
    const cookieName = cookieValue.split('=').shift();
    const cookieNameLength = cookieName.length;
    let cookieIndex = -1;
    cookies.forEach((value, index) => {
      if (`${value.substr(0, cookieNameLength)}=` === `${cookieName}=`) {
        cookieIndex = index;
      }
    });
    if (cookieIndex > -1) {
      cookies[cookieIndex] = `${cookieValue};`;
    } else {
      cookies.push(`${cookieValue};`);
    }
    this.cookies = cookies.join(' ').trim();
  },
};