ar_classes.rb

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

module Connections
  def self.extended(host)
    host.connection.execute <<-EOSQL
      CREATE TABLE #{host.table_name} (
        #{host.primary_key} integer PRIMARY KEY AUTOINCREMENT,
        associated_model_id integer,
        mockable_model_id integer,
        nonexistent_model_id integer
      )
    EOSQL

    host.reset_column_information
  end
end

class NonActiveRecordModel
  extend ActiveModel::Naming
  include ActiveModel::Conversion
end

class MockableModel < ActiveRecord::Base
  extend Connections
  has_one :associated_model
end

class SubMockableModel < MockableModel
end

class AssociatedModel < ActiveRecord::Base
  extend Connections
  belongs_to :mockable_model
  belongs_to :nonexistent_model, class_name: "Other"
end

class AlternatePrimaryKeyModel < ActiveRecord::Base
  self.primary_key = :my_id
  extend Connections
  attr_accessor :my_id
end