class Shoulda::ActiveRecord::Matchers::ValidationMatcher

def allows_value_of(value, message = nil)
  allow = AllowValueMatcher.
    new(value).
    for(@attribute).
    with_message(message)
  if allow.matches?(@subject)
    @negative_failure_message = allow.failure_message
    true
  else
    @failure_message = allow.negative_failure_message
    false
  end
end