How to stub or spy on a an inner function

[Gmiliuta]

Hello everyone,

We are using cypress for unit testing and we have a case where we need to stub/ spy an inner function as in example below.

// storage.js module

export function addDetails({ name, lastname }) {
      const allDetails =  JSON.parse(localStorage.getItem("personDetails"))
      allDetails.push(`${name} {lastname}`)
      
      localStorage.setItem("personDetails",  JSON.stringify(fullname))
      
      updateDetailsCount(allDetails)
}

export function updateDetailsCount(details) {
      // doing something with details
}

// stroage.cy.js unit test

import * as storageModule from './storage.js'

describe('addDetails', () => {
 
    it('should', () => {
        const name = 'tom';
        const lastname = 'jones'

        const updateDetailsCountSpy = cy.spy(storageModule, 'updateDetailsCount')

         storageModule.addDetails(name, lastname);

         expect(updateCartItemsCountSpy).to.have.been.called.once
    });
  });

I need to spy / stub updateDetailsCount when addDetails but above code is not working and I cannot figure out why and how to achieve this. Any help is appreciated! Thanks