activerecord_bug.rb

ACTIVE_RECORD_VERSION =
    'master'                # fails
#    '4.2.2'                # fails
#    '4.1.11'               # fails
#    '4.0.13'               # passes

if ACTIVE_RECORD_VERSION == 'master'
    
    require 'bundler/inline'

    gemfile(true) do
      source 'https://rubygems.org'
      gem 'rails', github: 'rails/rails'
      gem 'arel', github: 'rails/arel'
      gem 'sqlite3'
    end
else
    gem 'activerecord', ACTIVE_RECORD_VERSION 
end

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, force: true do |t|
  end

  create_table :comments, force: true do |t|
    t.integer :post_id
  end
end

class Post < ActiveRecord::Base
  has_many :comments
end

class Comment < ActiveRecord::Base
  belongs_to :post
  validates :post, presence: true
end

class BugTest < Minitest::Test

    def setup
        @post = Post.create!
    end
  
    # This test fails with newer versions of ActiveRecord
    def test_must_have_thing_id_when_created_from_association
        comment = @post.comments.create!
        comment.post_id = nil
        
        assert comment.invalid?
    end
  
    def test_must_have_thing_when_created_with_association
        comment = @post.comments.create!
        comment.post = nil
        
        assert comment.invalid?
    end
    
    def test_must_have_thing_id_when_created_with_thing_id
        comment = Comment.create!(post_id: @post.id)
        comment.post_id = nil
        
        assert comment.invalid?
    end
  
    def test_must_have_thing_id_when_created_with_thing
        comment = Comment.create!(post: @post)
        comment.post_id = nil
        
        assert comment.invalid?
    end
end