https://github.com/rails/rails/tree/master/guides/bug_report_templates

ar.rb

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"
  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  gem "rails", '~> 5.2'
  gem 'pry-rails'
  gem "sqlite3"
end

require "active_record"

ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")

ActiveRecord::Schema.define do
  create_table :topics, force: true do |t|
    t.string :title
  end
end

ActiveRecord::Base.logger = Logger.new(STDOUT)

class Topic < ActiveRecord::Base
end

binding.pry