How will we call a function written in a separate file from a Cypress test?

From https://docs.cypress.io/api/cypress-api/custom-commands.html

Put this in your support/commands.js file:

Cypress.Commands.add('subValues', (a, b) => { return a - b });

Put this in your support/index.js file, if it isn’t already there (it should be):

import "./commands";

Call it in your test like so:

describe ('Calling a function', function(){
  it('Call the Subtract function and asert the calculation', function(){
    cy
      .subValues(15, 8)
      .should('eq', 7) // true        
    });
});