ex: execute in shoulda tests

customer_test.rb

  context ".rent book with quantity" do
    setup do
      @book = Factory(:book, :quantity => 1)
      @customer = Factory(:customer)
    end
    
    execute do
      @customer.rent(@book)
    end
    
    should "create order for customer" do
      assert_equal 1, @customer.orders.size
    end
    
    should "decrement quantity for book" do
      assert_equal 0, @book.quantity
    end    
  end