After adding escape characters to the code,
clc;clear all;close all;
open_system(new_system('Test'));
system_name = 'Test';
%load_system('Robotics System Toolbox')
add_block('Robotics\ System\ Toolbox/ROS/Blank\ Message','Test/msg_1')
the error still persists
Error using test (line 7)
Error due to multiple causes.
Caused by:
Error using test (line 7)
'Robotics\ System\ Toolbox' is not a valid model name because it is not a valid MATLAB function name.
Error using test (line 7)
There is no block named 'Robotics\ System\ Toolbox/ROS/Blank\ Message'