rails/activemodel/test/cases/tests_database.rb

require 'logger'

activerecord_path = File.expand_path('../../../../activerecord/lib', __FILE__)
$:.unshift(activerecord_path) if File.directory?(activerecord_path) && !$:.include?(activerecord_path)

require 'active_record'

module ActiveModel
  module TestsDatabase
    mattr_accessor :connected

    def self.included(base)
      unless self.connected
        setup_connection
        setup_schema
      end

      base.send :include, ActiveRecord::TestFixtures
    end

    def self.setup_schema
      original, $stdout = $stdout, StringIO.new
      load(SCHEMA_FILE)
    ensure
      $stdout = original
      self.connected = true
    end

    def self.setup_connection
      defaults = { :database => ':memory:' }

      adapter = defined?(JRUBY_VERSION) ? 'jdbcsqlite3' : 'sqlite3'
      options = defaults.merge :adapter => adapter, :timeout => 500
      ActiveRecord::Base.establish_connection(options)
    end
  end
end