test.rb

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', '4.2.5'
  gem 'sqlite3'
end

require 'active_record'
require 'minitest/autorun'
require 'logger'

ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :products do |t|
    t.decimal :price, precision: 12, scale: 2
    t.references :content
  end

  create_table :contents do |t|
  end
end

class Product < ActiveRecord::Base
  belongs_to :content
end

class Content < ActiveRecord::Base
  has_one :product
end

class BugTest < Minitest::Test
  def setup
    Content.delete_all; Product.delete_all;
  end

  def test_negative_price
    Content.create(product: Product.create(price: -0.9))
    joined_product = Content.joins(:product).select('products.*').first
    product = Product.first
    assert_equal product.price?, joined_product.price?
  end

  def test_positive_price
    Content.create(product: Product.create(price: 0.9))
    joined_product = Content.joins(:product).select('products.*').first
    product = Product.first
    assert_equal product.price?, joined_product.price?
  end

  def test_nil_price
    Content.create(product: Product.create)
    joined_product = Content.joins(:product).select('products.*').first
    product = Product.first
    assert_equal product.price?, joined_product.price?
  end

  def test_zero_price
    Content.create(product: Product.create(price: 0))
    joined_product = Content.joins(:product).select('products.*').first
    product = Product.first
    assert_equal product.price?, joined_product.price?
  end
end