Mocha unit test on a non exported function returns 'xx is not a function'

Question

I'm trying to run a unit test on a non exported function using mocha, but it gives an error 'xx is not a function'. Sample structure is like the ff code, wherein I'd like to test the function isParamValid. The code format in settings.js already exists in our system so I cannot refactor it.

// settings.js
const settings = (() => {
  const isParamValid = (a, b) => {
    // process here
  }

  const getSettings = (paramA, paramB) => {
    isParamValid(paramA, paramB);
  }
  
  return {
    getSettings,
  }
})();

module.exports = settings;

I've tried the ff code to test it, but mocha gives the error ReferenceError: isParamValid is not defined

// settings.test.js
const settings= rewire('./settings.js');
describe('isParamValid', () => {
    it('should validate param', () => {
      let demo = settings.__get__('isParamValid');

      expect(demo(0, 1)).to.equal(true);
      expect(demo(1, 0)).to.equal(true);
      expect(demo(1, 1)).to.equal(false);
    })
  })

Answer 1

You can't directly access isParamValid here. Try to test it via integration as below

const settings = require('./settings.js'); // No need of rewire

describe('isParamValid', () => {
    it('should validate param', () => {
      const demo = settings.getSettings; // Read it from getSettings

      expect(demo(0, 1)).to.equal(true);
      expect(demo(1, 0)).to.equal(true);
      expect(demo(1, 1)).to.equal(false);
    })
})