To chech the url is valid when using Net::HTTP.get_response(

I am using Net::HTTP.get_response( URI.parse( url ) ) to get the reponse
from
a website. I have to test it with invalid url. How can i handle it if an
ivalid url is provided and to give and error message.

def method

  response = Net::HTTP.get_response( URI.parse( url ) )

  r = 3; while r> 0 and
    ( response.is_a? Net::HTTPFound or
      response.is_a? Net::HTTPSeeOther )

  location = URI.parse( response[ 'location' ] )

  cookie = response.get_fields( 'Set-Cookie' )

  cookie.map! { | c | c.split( ';' ).first }

  cookie = cookie.join( '; ' )

end