How to test Sequelize 'afterCreate' hook that sends email using nodemailer?

I have a User sequelize model that's loaded using the index.js file in the models directory e.g.

"use strict";

var fs        = require("fs");
var path      = require("path");
var Sequelize = require("sequelize");
var basename  = path.basename(module.filename);
var env       = process.env.NODE_ENV || "development";
var config    = require(__dirname + '/../../config/database.json')[env];
var sequelize = new Sequelize(config.database, config.username, config.password, config);
var db        = {};

fs
  .readdirSync(__dirname)
  .filter(function(file) {
   return (file.indexOf(".") !== 0) && (file !== basename);
 })
  .forEach(function(file) {
     var model = sequelize["import"](path.join(__dirname, file));
     db[model.name] = model;
 });

Object.keys(db).forEach(function(modelName) {
   if ("associate" in db[modelName]) {
   db[modelName].associate(db);
  }
});

 db.sequelize = sequelize;
 db.Sequelize = Sequelize;

 module.exports = db;

In my models afterSave hook:

afterCreate : function(user, options, fn){
  mailer.sendEmailConfirmation(user.email, user.confirmation_code,   function(err){
      if(err){
        console.log(err);
      }
    });

    fn(null, user);
  } 

mailer is a dependency required in the model. How do I go about unit testing this? I basically want to save the user in a mocha test and ensure the sendEmailConfirmation is called.