test.rb

#!/usr/bin/env ruby

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 'pg'
  gem 'sequel'
  gem 'minitest'
  gem 'minitest-hooks'
  gem 'database_cleaner-sequel'
end

system("sudo -u postgres dropdb --if-exists check_sequel_db")
system("sudo -u postgres createdb check_sequel_db")

DB_URL="postgres://postgres:postgres@localhost:5432/check_sequel_db"
DB = Sequel.connect(DB_URL)

DB.create_table(:insiders, :ignore_index_errors=>true) do
  primary_key :id
  Integer :number_of_shares, :null=>false
end

class Insider < Sequel::Model
end

ENV['RACK_ENV'] = 'test'
require 'minitest/autorun'
require 'minitest/pride'
require 'database_cleaner-sequel'

DatabaseCleaner[:sequel].strategy = :truncation

class Minitest::Test
  def before_setup
    DatabaseCleaner[:sequel].start
  end

  def after_teardown
    DatabaseCleaner[:sequel].clean
  end
end

require 'logger'

LOGGER = Logger.new($stdout)
DB.loggers << LOGGER

describe 'insider' do
  it 'test postgres read committed mode default lock' do
    Insider.create(number_of_shares: 200)

    puts "Insider count outer thread: #{Insider.count}"

    thread1 = Thread.new do
      sleep rand(0.1..0.2)
      DB.transaction do
        puts "Insider count inner first thread: #{Insider.count}"
        insider_1 = Insider.last
        insider_1.update(number_of_shares: insider_1.number_of_shares - 10)
      end
    end

    thread2 = Thread.new do
      sleep rand(0.1..0.2)
      DB.transaction do
        insider_2 = Insider.last
        insider_2.update(number_of_shares: insider_2.number_of_shares - 10)
      end
    end

    thread1.join
    thread2.join

    assert_equal 180.0, Insider.last.number_of_shares
  end
end