AR in memory

in_memory.rb

require "active_record"
require "sqlite3"

ActiveRecord::Base.establish_connection(
  :adapter => 'sqlite3',
  :host => "localhost",
  :database => ':memory:'
)

ActiveRecord::Schema.define do
  create_table :posts do |t|
    t.column :title, :string
  end
end

class Post < ActiveRecord::Base
end

Post.create!(title: 'foo')