Reproduction script for Rails issue 17325

17325

unless File.exist?('Gemfile')
  File.write('Gemfile', <<-GEMFILE)
    source 'https://rubygems.org'
    source 'https://rubygems.org'
    gem 'rails', github: 'rails/rails'
    gem 'devise', github: 'plataformatec/devise'
    gem 'arel', github: 'rails/arel'
    gem 'sqlite3'
  GEMFILE

  system 'bundle'
end

require 'bundler'
Bundler.setup(:default)

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

# 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 :title
  end

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

class Post < ActiveRecord::Base
  has_one :comment
end

class Comment < ActiveRecord::Base
  validates_presence_of :post_id
  belongs_to :post
end

class BuildOneAssociationTest < ActiveSupport::TestCase
  def test_build_should_not_trigger_save
    post = Post.create!
    post.comment = Comment.create!({post_id: post.id})
    # This is going to fail because it is trying to save the original comment
    # whose foreign_key was already sit to nil, making it invalid per validations.
    post.build_comment
  end
end