better_test_cookies.rb

# Include this in your RAILS_ROOT/test/test_helper.rb

class ActionController::TestCase
  def better_cookies
    cookies = {}
    Array(@response.headers['Set-Cookie']).each do |cookie|
      key = nil
      details = cookie.split(';').inject({}) do |fields, cookie_field|
        pair = cookie_field.split('=').map {|val| Rack::Utils.unescape(val.strip)}
        key = pair.first unless key
        fields.merge(pair.first => pair.last)
      end
      details['expires'] = Time.parse(details['expires']) if details['expires']
      cookies[key] = details
    end
    cookies
  end
end

# Use it with something like…
# assert better_cookies['token']['expires'].present? &&
#        better_cookies['token']['expires'] > 13.days.from_now