Cypress setup for conditional WordPress login. (Double dashes in file names should be replaced with slashes)

cypress--support--commands.js

// ***********************************************
// This example commands.js shows you how to
// create various custom commands and overwrite
// existing commands.
//
// For more comprehensive examples of custom
// commands please read more here:
// https://on.cypress.io/custom-commands
// ***********************************************
//
//
// -- This is a parent command --
// Cypress.Commands.add("login", (email, password) => { ... })
//
//
// -- This is a child command --
// Cypress.Commands.add("drag", { prevSubject: 'element'}, (subject, options) => { ... })
//
//
// -- This is a dual command --
// Cypress.Commands.add("dismiss", { prevSubject: 'optional'}, (subject, options) => { ... })
//
//
// -- This is will overwrite an existing command --
// Cypress.Commands.overwrite("visit", (originalFn, url, options) => { ... })

Cypress.Commands.add('login', (username, password) => {
    cy.getCookies().then(cookies => {
        let hasMatch = false;
        cookies.forEach((cookie) => {
            if (cookie.name.substr(0, 20) === 'wordpress_logged_in_') {
                hasMatch = true;
            }
        });
        if (!hasMatch) {
            cy.visit('/wp-login.php').wait(1000);
            cy.get('#user_login').type(username);
            cy.get('#user_pass').type(`${password}{enter}`);
        }
    });
});

cypress--support--index.js

// ***********************************************************
// This example support/index.js is processed and
// loaded automatically before your test files.
//
// This is a great place to put global configuration and
// behavior that modifies Cypress.
//
// You can change the location of this file or turn off
// automatically serving support files with the
// 'supportFile' configuration option.
//
// You can read more here:
// https://on.cypress.io/configuration
// ***********************************************************

// Import commands.js using ES2015 syntax:
import './commands';

Cypress.Cookies.defaults({
    whitelist: /wp|wordpress/
});

before(() => {
    cy.login(Cypress.env('wpUsername'), Cypress.env('wpPassword'));
});

cypress.env.json

{
  "wpUsername": "username",
  "wpPassword": "password"
}

Great, simple code, cheers!