After refactoring #2 - modified

errorize.js

import Ember from 'ember';

var errorize = Ember.Object.extend({
  init() {
    this._super();
    this.set('errorsList', {});
  },

  // test should check various inputs and verify addToErrorsList is called with proper arguments
  processError(error) {
    let field = (/\w+$/.exec(error.source.pointer))[0].camelize();
    let message = error.detail;
    this.addToErrorsList(field, message);
  },

  // test should verify adding new field and appending error to existing field
  addToErrorsList(field, message) {
    (this.get('errorsList')[field] = this.get('errorsList')[field] || [])
      .push({message});
  },

  // test should verify empty and not-empty case
  serialize() {
    this.get('errors.responseJSON.errors').forEach(this.processError);
    return this.get('errorsList');
  },
});

export default errorize;