anchor.diff:      ok.
   
   
  -code_change( _OldVsn, State, _Extra ) ->
  -    % FIXME - call the implementation's code_change
  -    { ok, State }.
  +code_change( OldVsn, State, Extra ) ->
  +    call_impl( code_change, [ OldVsn, State#state.context, Extra ], State ).
   
   
   %% ===================================================================
  
positive.code:       fun mock_impl_module_stop/1,
        [ fun test_start_device/1
        , fun test_get_event/1
        %, fun test_stop_device/1
        ]
      }.
  
negative.code:     Action = impl_func_to_action_name( Func ),
      handle_impl_result( Result, Action, State, Tag ).
  
  handle_impl_result( { ok, Context }, code_change, State, _Tag ) ->
      NewState = State#state{ context = Context },
      { ok, NewState };
  
  handle_impl_result( { error, _ } = Result, code_change, _State, _Tag ) ->
      Result;
  
  handle_impl_result( { ok, Result, Context }, Action, State, Tag ) ->
      NewState = State#state{ context = Context },
      send_owner( NewState, Action, { ok, Result }, Tag ),
  