Test plain javascript file returning different objects

Question

Is it possible to test the code below with Jasmine testing tool or any other npm module like rewire or similar?

const AuthValidatorDumb = require('./src/AuthValidatorDumb');
const AuthValidator = require('./src/AuthValidator');
const config = require('../config');

let instance;

if (!instance) {
  if (config.get('auth.enabled')) {
    instance = AuthValidator;
  } else {
    instance = AuthValidatorDumb;
  }
}

module.exports = instance;

Answer 1

I've got a variant for testing the code above.Suppose you have:

1) The code for index.js in the question above.

2) AuthValidator.js :

class AuthValidator {}
module.exports = AuthValidator;

3) AuthValidatorDumb.js :

class AuthValidatorDumb {}
module.exports = AuthValidatorDumb;

Here is test/index.spec.js :

const proxyquire = require('proxyquire');
const AuthValidator = require('../src/AuthValidator');
const AuthValidatorDumb = require('../src/AuthValidatorDumb');

describe('auth index', () => {
  it('should return AuthValidator', () => {
    const configMock = { get: () => 'sth' };
    const Instance = proxyquire('../index', {
      '../config': configMock,
    });
    expect(new Instance() instanceof AuthValidator).toBeTruthy();
  });

  it('should return AuthValidatorDumb', () => {
    const configMock = { get: () => undefined };
    const Instance = proxyquire('../index', {
      '../config': configMock,
    });
    expect(new Instance() instanceof AuthValidatorDumb).toBeTruthy();
  });
});