I've been using variations of this for years to help figure out little problems with ActiveRecord.

active_record_playground.rb

require 'rubygems'
require 'active_record'
require 'logger'

ActiveRecord::Base.establish_connection({:adapter => "sqlite3", :database => ":memory:"})

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

ActiveRecord::Schema.define do
  create_table :people do |t|
    t.string :first_name, :last_name
  end
  
  create_table :addresses do |t|
    t.integer :person_id
    t.string :street, :city, :state, :postal_code, :label
  end
  
  add_index :addresses, :label
end

class Person < ActiveRecord::Base
  has_many :addresses
end

class Address < ActiveRecord::Base
  belongs_to :person
  scope :labeled, lambda {|name| where(:label => name)}
end

require 'test/unit'
require 'contest'

class PersonTest < ActiveSupport::TestCase
  context "Person with a home and school address" do
    setup do
      @user = Person.create(:first_name => "Jacob", :last_name => "Rasmussen")
      @home = @user.addresses.create(:street => "3434 Maple Ave.", :city => "Austin", :state => "TX", :postal_code => "78743", :label => "Home")
      @school = @user.addresses.create(:street => "4343 Oak Blvd.", :city => "Austin", :state => "TX", :postal_code => "77878", :label => "School")
    end
    
    test "should have a home address" do
      assert_equal @home, @user.addresses.labeled("Home").first
    end
  end
end

I've been using variations of this for years to help figure out little problems with ActiveRecord.