const $internals = {
hystrix: (...){},
runCmd: (...){},
init: (options) => {

  /* Setup logger */
  $internals.log = wsLogger(options.constants);
  /* Setup Hystrix functions */
  const hystrixFunctions = $internals.hystrix(options, client);

  return {
    registrationUser: (req, data) => {
      return $internals.runCmd({
        endpoint: 'registrationUser',
        req,
        data,
        executeFn: hystrixFunctions.hRegistrationUser
      });
    }
  };
}
}

module.exports = (options = {}) => {

if (Object.keys(options).length === 0)
  options = $default;

assert(options);
assert(options.constants);

return $internals.init(options);
};

...
  const registrationService = require('../service/service');
  ...

describe('POST /api/v1/user', () => {
it.only('should register new user', (done) => {
  const userRegistration = sinon.stub(registrationService, 'registrationUser');
  const params = {
    name: 'Dummy Name',
    number: '8726853453',
    password: 'myTestPass',
    verificationMode: 'OTP',
    otp: 'otp',
    sim: 'sim',
    email: 'user.me@io',
    code: 'code',
    answer: 'answer'
  }
  request(server)
    .post('/api/v1/user')
    .set('Content-Type', 'application/json')
    .send(params)
    .end((err, res) => {
      should.not.exist(err);
      sinon.assert.calledOnce(userRegistration);
      done();
    });
  })
})