test.js

var sinon = require('sinon');

var Promise = require('bookshelf/dialects/base/promise').Promise;
var Bookshelf = require('bookshelf');

var unhandled = sinon.spy();
var caught = sinon.spy();

Promise.onPossiblyUnhandledRejection(unhandled);

var MySql = Bookshelf.initialize({
  client: 'mysql',
  connection: {
    host     : '127.0.0.1',
    user     : 'root',
    password : '',
    database : 'testdb',
    charset  : 'utf8'
  }
});

var User = MySql.Model.extend({

  tableName: 'users',
  
  initialize: function(){
    this.on('saving', validate);
  }

});

var validate = function (){
  throw new Error('this is always thrown!');
};


new User().save().catch(caught).finally(function () {
  console.log(unhandled.called); // => false
});

process.nextTick(function () {
  console.log(caught.called) // => true
  console.log(unhandled.called); // => true
});