Rails 4.1.x ActiveRecord serialize as JSON failing test

rails_serialize_411_bug.rb

gem 'activerecord', '4.1.1'
require 'active_record'
require 'minitest/autorun'
require 'logger'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :posts do |t|
    t.string  "comment"
  end

  create_table :comments do |t|
    t.integer :post_id
  end
end

class Post < ActiveRecord::Base
  serialize :comment, JSON
end

class Comment
  include ActiveModel::Model
  attr_accessor :category, :text
end

class BugTest < Minitest::Test
  def test_association_stuff
    post = Post.create!
    post.comment = Comment.new(category: "test", text: "Test is a test")
    post.save!

    assert post.comment.is_a?(Hash), "This is a hash in 4.0.x, but not in 4.1.x"
    assert_equal "test", post.comment["category"]

  end
end