class Shoulda::ActiveRecord::Matchers::ValidationMatcher

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