Process doesn't terminate even ZeroMQ socket closed

I'm making a publish subscribe using ZeroMQ. Here is a simplified code :

import zmq from 'zeromq';
import d from 'debug';

const debug = d('publisher');

let port = '8000';
let subject = 'FLIGHTS';

const socket = zmq.socket('pub');

socket.on('close', function(...toto) {
  debug('connection closed');
});
socket.on('close_error', function(...toto) {
  debug('error while closing connexion');
});

socket.monitor(10, 0);
socket.bindSync('tcp://*:' + port);

export function send(message: object) {
  const jsonMessage = JSON.stringify(message);
  socket.send([subject, jsonMessage]);
}

export function close() {
  socket.close();
}

setTimeout( () =>
close()
, 3000 );

The problem I have is that the process won't exit even if the socket is closed after 3 seconds. I can't use process.exit because the module I'm making is used in a lot a jest tests. I didn't find anything in the ZeroMQ documentation. Can you help me, please ?

Thanks in advance.

via Alexandre DERNIAME