How can we test the alert and the text it is displaying using Cypress.io Js automation framework?

How can we test the alert and text inside is displaying using Cypress.io Js automation framework? I am unable to figure out the relevant example in Cypress documentation, please advise.

describe('Test an alert and the text displaying', function() {
it('Verify alert and its text content', function(){
    cy.visit('http://www.seleniumeasy.com/test/javascript-alert-box-demo.html')     
    cy.get('button').contains('Click me!').click()
    cy.on ('window:alert', 'I am an alert box!')    

    })

})

Answer

Figured out the answer using cy.stub() method as advised by Richard Matsen:

describe('Test an alert and the text displaying', function() {
it('Verify alert and its text content', function(){
    cy.visit('http://www.seleniumeasy.com/test/javascript-alert-box-demo.html')    

    const stub = cy.stub()  
    cy.on ('window:alert', stub)
    cy
    .get('button').contains('Click me!').click()
    .then(() => {
      expect(stub.getCall(0)).to.be.calledWith('I am an alert box!')      
    })  

    })

})