sendou.ink/cypress/support/index.d.ts

// in cypress/support/index.d.ts
// load type definitions that come with Cypress module
/// <reference types="cypress" />

declare namespace Cypress {
  interface Chainable {
    /**
     * Custom command to select DOM element by data-cy attribute.
     * @example cy.dataCy('greeting')
     */
    dataCy(value: string): Chainable<Element>;
    /**
     * Mock login
     * @example cy.login('sendou')
     */
    login(user: "sendou" | "nzap"): Chainable<Element>;
  }
}