Parse URL to see if it's an image

uri_parser.rb

class UriParser
  def self.uri_is_image?(uri)
    case File.extname(uri.path)
    when '.jpg', '.png', '.gif'
      return true
    else 
      return false
    end
  end
end

uri_parser_spec.rb

describe UriParser
  describe '.uri_is_image?' do
    it 'returns true when the URL is a jpg' do
      uri = URI('http://www.chuckg.org/images/logo.jpg')
      Scraper.send(:uri_is_image?, uri).should be_true
    end
    it 'returns true when the URL is a png' do
      uri = URI('http://www.chuckg.org/images/logo.png')
      Scraper.send(:uri_is_image?, uri).should be_true
    end
    it 'returns true when the URL is a gif' do
      uri = URI('http://www.chuckg.org/images/logo.gif')
      Scraper.send(:uri_is_image?, uri).should be_true
    end
    it 'returns false when the URL is not an image' do
      uri = URI('http://www.chuckg.org/blog/blah/blahjpg?test=true')
      Scraper.send(:uri_is_image?, uri).should be_false
    end
  end
end