text: const net = require('net');
  
  const PORT = 9999;
  const noop = _ => _;
  let server;
  
  exports.noop = noop;
  exports.serverPort = PORT;
  exports.startServer = (done) => {
    if (server) {
      return done();
    }
    server = net.createServer((socket) => {
      socket.on('error', noop);
      socket.on('data', (data) => {
        if (`${data}` === 'error') {
          socket.destroy();
        } else {
          socket.write(data);
        }
      });
    });
    server.listen(PORT, done);
    server.unref();
    return server;
  };
  