Sample test showcasing unexpected nested transaction handling in Rails

nested-rollback-failure.rb

# frozen_string_literal: true

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"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", github: "rails/rails"
  gem "sqlite3"
end

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, force: true do |t|
    t.string :title, null: false
  end
end

# Uncomment this module to apply patch to test how it affects test results.
#
# module ActiveRecordPatch
  # def transaction(requires_new: nil, isolation: nil, joinable: true)
    # if !requires_new && current_transaction.joinable?
      # if isolation
        # raise ActiveRecord::TransactionIsolationError, "cannot set isolation when joining a transaction"
      # end

      # yield
    # else
      # transaction_manager.within_new_transaction(isolation: isolation, joinable: joinable) { yield }
    # end
  # rescue ActiveRecord::Rollback
    # # NOTE: This is what was added to the original implementation
    # raise if !requires_new && current_transaction.joinable?
  # end
# end
# module ActiveRecord
  # module ConnectionAdapters # :nodoc:
    # class SQLite3Adapter
      # prepend ActiveRecordPatch
    # end
  # end
# end

class Post < ActiveRecord::Base
end

class MyError < StandardError
end

class BugTest < Minitest::Test
  def test_rollback_error
    ActiveRecord::Base.transaction do
      Post.create(title: 'first')
      ActiveRecord::Base.transaction do
        Post.create(title: 'second')
        raise ActiveRecord::Rollback
      end
      Post.create(title: 'last')
    end

    assert_nil(Post.find_by(title: 'first'))
    assert_nil(Post.find_by(title: 'second'))
    assert_nil(Post.find_by(title: 'last'))
  end
end