Trying to validate a boolean in ActiveRecord

bla.rb

# == Schema Information
#
# Table name: Bla
#  test       :boolean

class Bla < ActiveRecord::Base
  attr_accessible :test
  before_validation :test_present
  def test_present
  	puts "TEST PRESENT"
  	puts self.test
  	errors.add(:test, "Must be set to true or false") if !([true, false].include?(self.test))
  end
  
# Same behavior with validate, before_save, before_validation:
b = Bla.new
b.test = "bla"
b.save
# prints
# TEST PRESENT
# false

# found out about this while testing
# 	it {should_not allow_value(:other).for(:completed)}
# I know that I don't need to test that the boolean will be true or false, the db does it for me...
# but I'm wondering... does the test attribute ever get to be "bla"?