it does work

exceptions.rb

module Exceptions 

  # custom exceptions / errors with custom default messages a-go-go

  # the base for defined errors. 
  class DefinedError < RuntimeError 
    @msg = "Undefined Defined Error" 
 
    def message 
      return @msg || super 
    end 
  end 
 
  class MileageError < DefinedError 
    def initialize(message = "The supplied mileage is invalid") 
      @msg = message 
    end 
  end 
       
  class DateError < DefinedError 
    def initialize(message = "The supplied date is invalid") 
      @msg = message 
    end 
  end 
 
  class FollowError < DefinedError 
    def initialize(message = "You cannot follow that car") 
      @msg = message 
    end 
  end 
 
end