test_new.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 'database_cleaner-sequel'
end

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

DB = Sequel.postgres("check_sequel_db")

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

# require 'logger'

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

describe 'insider' do
  it 'test postgres read committed mode default lock' do
    100.times do |i|
      sleep 1
      puts i+1
      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
end