Solve some warnings and a failing test.

actionpack/lib/action_controller/test_case.rb

@@ -191,6 +191,7 @@ module ActionController
     DEFAULT_OPTIONS = Rack::Session::Abstract::ID::DEFAULT_OPTIONS
 
     def initialize(session = {})
+      @env, @by = nil, nil
       replace(session.stringify_keys)
       @loaded = true
     end

actionpack/lib/action_dispatch/http/request.rb

@@ -199,7 +199,7 @@ module ActionDispatch
     # TODO This should be broken apart into AD::Request::Session and probably
     # be included by the session middleware.
     def reset_session
-      session.destroy if session
+      session.destroy if session && session.respond_to?(:destroy)
       self.session = {}
       @env['action_dispatch.request.flash_hash'] = nil
     end